PLT-4457 Added AtMention component to better render at mentions (#6563)

* Moved Utils.searchForTerm into an action

* Added easier importing of index.jsx files

* PLT-4457 Added AtMention component to better render at mentions

* Fixed client unit tests

* Fixed merge conflict

* Fixed merge conflicts

webapp/package.json

@@ -15,6 +15,7 @@
     "flux": "3.1.2",
     "font-awesome": "4.7.0",
     "highlight.js": "9.11.0",
+    "html-to-react": "1.2.9",
     "inobounce": "0.1.4",
     "intl": "1.2.5",
     "jasny-bootstrap": "3.1.3",