Enable Caching/Prefetching for messages, groups, etc.

[JustinLovesCompsci]

Use local cache or Parse localDataStore to cache messages and groups data. Use real push notification to notify data changes from server to client app. This removes unnecessary network requests and make the app faster for UI responds.
May even prefetch ~20 messages for every group displayed in the main view before entering a group. The goal is to eliminate network request delay when entering a group to chat