Change panel references to popup

Panels have been deprecated for a long time, and when creating them a
popup is created instead, so this change introduces the following:

- Instead of trying to create a panel, create a popup directly
- Change all i18n strings so "popups" are mentioned instead of "panels"
- Change the |uniquetab| option so it is now set to "popup" instead of
  "panel", while being backwards-compatible with the "panel" value.
- Change the default |uniquetab| option to "popup", because users seem
  to like this option the most (impression from the CWS reviews).

Fixes: #13
Change-Id: I67aea8168013dd4b77d4ea4229179bcd5145cb6d
diff --git a/src/js/options.js b/src/js/options.js
index b502450..9fc10df 100644
--- a/src/js/options.js
+++ b/src/js/options.js
@@ -45,7 +45,7 @@
     if (isEmpty(items)) {
       items = {
         translateinto: {},
-        uniquetab: '',
+        uniquetab: 'popup',
       };
       chrome.storage.sync.set(items);
     }
@@ -53,14 +53,10 @@
     // Check the checkbox of the window opening
     if (items.uniquetab === 'yep') $('#uniquetab').checked = true;
     if (items.uniquetab === '') $('#varioustabs').checked = true;
-    if (items.uniquetab === 'panel') $('#panel').checked = true;
+    if (items.uniquetab === 'panel' || items.uniquetab === 'popup')
+      $('#popup').checked = true;
 
     // Add event listeners for certain buttons and links
-    $('#panelsflag').addEventListener('click', _ => {
-      event.preventDefault();
-      chrome.tabs.create({url: 'chrome://flags/#enable-panels'});
-    });
-
     $('#save').addEventListener('click', _ => {
       saveOptions(true);
     });