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/utils/constants.jsx

@@ -193,7 +193,9 @@ export const ActionTypes = keyMirror({
 
     BROWSER_CHANGE_FOCUS: null,
 
-    EMOJI_POSTED: null
+    EMOJI_POSTED: null,
+
+    RECEIVED_PLUGIN_COMPONENTS: null
 });
 
 export const WebrtcActionTypes = keyMirror({