Experimental implementation for webapp plugins (#7185)

* Start of experimental implementation for webapp plugins

* Updates to webapp plugin architecture

* Update pluggable test

* Remove debug code

webapp/package.json

@@ -25,7 +25,7 @@
     "localforage": "1.5.0",
     "marked": "mattermost/marked#5194fc037b35036910c6542b04bb471fe56b27a9",
     "match-at": "0.1.0",
-    "mattermost-redux": "mattermost/mattermost-redux#webapp-4.1",
+    "mattermost-redux": "mattermost/mattermost-redux#master",
     "object-assign": "4.1.1",
     "pdfjs-dist": "1.9.441",
     "perfect-scrollbar": "0.7.1",