diff --git a/src/js/common.js b/src/js/common.js
new file mode 100644
index 0000000..445016e
--- /dev/null
+++ b/src/js/common.js
@@ -0,0 +1,242 @@
+/**
+  * Functions hasClass(), addClass() and removeClass() developed by Jake Trent (http://jaketrent.com/post/addremove-classes-raw-javascript/)
+  */
+function hasClass(el, className) {
+  if (el.classList)
+    return el.classList.contains(className)
+  else
+    return !!el.className.match(new RegExp('(\\s|^)' + className + '(\\s|$)'))
+}
+
+function addClass(el, className) {
+  if (el.classList)
+    el.classList.add(className)
+  else if (!hasClass(el, className)) el.className += " " + className
+}
+
+function removeClass(el, className) {
+  if (el.classList)
+    el.classList.remove(className)
+  else if (hasClass(el, className)) {
+    var reg = new RegExp('(\\s|^)' + className + '(\\s|$)')
+    el.className=el.className.replace(reg, ' ')
+  }
+}
+
+// MultiSelect implementation:
+var MultiSelect = function MultiSelect(element) {
+  this.element_ = element;
+  this.selected_ = [];
+
+  var forElId = this.element_.getAttribute("for") || this.element_.getAttribute("data-for");
+  if (forElId) {
+    this.forEl_ = (forElId ? document.getElementById(this.element_.getAttribute("for")) : null);
+  }
+
+  this.init();
+};
+
+MultiSelect.prototype.renderSummary = function() {
+  if (this.forEl_) {
+    this.forEl_.innerText = this.selected_.join(", ") || "-";
+  }
+};
+
+MultiSelect.prototype.init = function() {
+  if (this.element_) {
+    this.element_.addEventListener("click", e => {
+      e.stopImmediatePropagation();
+    }, true);
+
+    this.element_.querySelectorAll(".mdl-custom-multiselect__item").forEach(item => {
+      var checkbox = item.querySelector("input[type=\"checkbox\"]");
+      var label = item.querySelector(".mdl-checkbox__label").innerText;
+      checkbox.addEventListener("change", e => {
+        if(checkbox.checked) {
+          this.selected_.push(label);
+        } else {
+          this.selected_ = this.selected_.filter(item => item !== label);
+        }
+        this.renderSummary();
+
+        var customEvent = new Event('custom-multiselect-change');
+        this.element_.dispatchEvent(customEvent);
+      });
+    });
+  }
+};
+
+var dynDialog = {
+  didItInit: false,
+  dialog: null,
+  url: null,
+  load: function(url, reload) {
+    if (this.didItInit === false) {
+      this.init();
+    }
+
+    if (this.url == url && reload !== true) {
+      this.show();
+      return;
+    }
+
+    this.url = url;
+
+    fetch(url).then(response => response.text()).then(response => {
+      if (this.dialog.open) {
+        this.close();
+      }
+
+      this.dialog.innerHTML = response;
+      componentHandler.upgradeElements(this.dialog);
+
+      this.dialog.querySelectorAll("[data-required]").forEach(input => {
+        input.setAttribute("required", "true");
+      });
+
+      var script = this.dialog.querySelectorAll("dynscript");
+      if (script.length > 0) {
+        for (var i = 0; i < script.length; i++) {
+          eval(script[i].innerText);
+        }
+      }
+      this.dialog.querySelectorAll("[data-dyndialog-close]").forEach(btn => {
+        btn.addEventListener("click", e => {
+          e.preventDefault();
+          this.close();
+        });
+      });
+
+      this.dialog.showModal();
+    });
+  },
+  reload: function() {
+    this.load(this.url, true);
+  },
+  show: function() {
+    this.dialog.showModal();
+  },
+  close: function() {
+    this.dialog.close();
+  },
+  init: function() {
+    this.dialog = document.createElement("dialog");
+    this.dialog.setAttribute("id", "dynDialog");
+    this.dialog.setAttribute("class", "mdl-dialog");
+    dialogPolyfill.registerDialog(this.dialog);
+    document.body.appendChild(this.dialog);
+
+    this.didItInit = true;
+  }
+};
+
+// From nodep-date-input-polyfill
+function isDateInputSupported() {
+  const input = document.createElement("input");
+  input.setAttribute("type", "date");
+
+  const notADateValue = "not-a-date";
+  input.setAttribute("value", notADateValue);
+
+  return (input.value !== notADateValue);
+}
+
+document.addEventListener("DOMContentLoaded", function() {
+  var dialogs = document.querySelectorAll("dialog");
+  for (var i = 0; i < dialogs.length; i++) {
+    dialogPolyfill.registerDialog(dialogs[i]);
+  }
+
+  document.querySelectorAll("[data-dyndialog-href]").forEach(link => {
+    link.addEventListener("click", e => {
+      e.preventDefault();
+      dynDialog.load(link.getAttribute("data-dyndialog-href"));
+    });
+  });
+
+  document.querySelectorAll(".mdl-custom-multiselect-js").forEach(menu => {
+    new MultiSelect(menu);
+  });
+});
+
+function importCSS(url) {
+  var link = document.createElement("link");
+  link.setAttribute("rel", "stylesheet");
+  link.setAttribute("href", url);
+  document.head.appendChild(link);
+}
+
+var loadScriptAsync = function(uri) {
+  return new Promise((resolve, reject) => {
+    var script = document.createElement('script');
+    script.src = uri;
+    script.async = true;
+    script.onload = () => {
+      resolve();
+    };
+    document.head.appendChild(script);
+  });
+}
+
+function hasParentDialog(el) {
+  while (el != document.documentElement) {
+    if (el.tagName == "DIALOG") {
+      return el;
+    }
+
+    el = el.parentNode;
+  }
+
+  return undefined;
+}
+
+function polyfillDateSupport(container) {
+  container.querySelectorAll("input[type=\"date\"]").forEach(el => {
+    el.setAttribute("type", "text");
+
+    dialogParent = hasParentDialog(el);
+
+    var options = {
+      format: "yyyy-mm-dd",
+      todayHighlight: true,
+      weekStart: 1,
+      zIndexOffset: 100,
+      container: dialogParent || container
+    };
+
+    if (el.hasAttribute("max")) {
+      options.endDate = el.getAttribute("max");
+    }
+
+    $(el).datepicker(options);
+  });
+
+  container.querySelectorAll("input[type=\"time\"]").forEach(el => {
+    el.setAttribute("placeholder", "hh:mm");
+  });
+}
+
+function initPolyfillDateSupport() {
+  console.info("Polyfilling date support");
+
+  importCSS("https://unpkg.com/bootstrap-datepicker@1.9.0/dist/css/bootstrap-datepicker3.standalone.min.css", "css");
+
+  loadScriptAsync("https://unpkg.com/jquery@3.4.1/dist/jquery.min.js", "js").then(_ => {
+    return loadScriptAsync("https://unpkg.com/bootstrap-datepicker@1.9.0/dist/js/bootstrap-datepicker.min.js");
+  }).then(_ => {
+    return loadScriptAsync("https://unpkg.com/bootstrap-datepicker@1.9.0/dist/locales/bootstrap-datepicker.es.min.js");
+  }).then(_ => {
+    console.log("[Date polyfill] Scripts loaded.");
+    polyfillDateSupport(document.documentElement);
+  });
+}
+
+window.addEventListener("load", function() {
+  document.querySelectorAll("[data-required]").forEach(input => {
+    input.setAttribute("required", "true");
+  });
+
+  if (!isDateInputSupported()) {
+    initPolyfillDateSupport();
+  }
+});