Add post list container to hold mounted post lists for faster rendering/channel switching.

web/react/utils/constants.jsx

@@ -9,6 +9,7 @@ module.exports = {
 
         CLICK_CHANNEL: null,
         CREATE_CHANNEL: null,
+        LEAVE_CHANNEL: null,
         RECIEVED_CHANNELS: null,
         RECIEVED_CHANNEL: null,
         RECIEVED_MORE_CHANNELS: null,