Implement workflow execution UI and logic

This CL adds a provisional workflow execution UI (which will need to be
thoroughly improved in the future), and most importantly the logic for
running workflows and actions inside workflows.

Bug: twpowertools:74
Change-Id: I94944a623a2411bef9d2b5244fea707e69a49790
diff --git a/package.json b/package.json
index b033fc6..01a4ae3 100644
--- a/package.json
+++ b/package.json
@@ -40,6 +40,7 @@
   },
   "private": true,
   "dependencies": {
+    "@material/mwc-circular-progress": "^0.27.0",
     "@material/mwc-dialog": "^0.27.0",
     "@material/tooltip": "^12.0.0",
     "@material/web": "^0.1.0-alpha.0",