Reapply "Merge pull request !2870 from rhodecode-enterprise-ce Polymer-lit-migration-1"

This reverts commit 2aebe6862d.

grunt_config.json

@@ -102,10 +102,23 @@
       "nonull": true
     }
   },
-  "uglify": {
+  "terser": {
     "dist": {
-      "src": "<%= dirs.js.dest %>/scripts.js",
-      "dest": "<%= dirs.js.dest %>/scripts.min.js"
+      "options": {
+        "compress": {
+          "ecma": 6
+        },
+        "mangle": {
+          "keep_classnames": true,
+          "keep_fnames": false
+        },
+        "output": {
+          "ecma": 6
+        }
+      },
+      "files": {
+        "<%= dirs.js.dest %>/scripts.min.js": "<%= dirs.js.dest %>/scripts.js"
+      }
     }
   },
   "less": {
@@ -156,7 +169,6 @@
       "tasks": [
         "less:development",
         "less:components",
-        "concat:polymercss",
         "webpack",
         "concat:dist"
       ]
@@ -169,7 +181,6 @@
       ],
       "tasks": [
         "less:components",
-        "concat:polymercss",
         "webpack",
         "concat:dist"
       ]