Refactors/removes prototype additions to base JS objects

* It wasn't a good idea
Helpers can verify any Mongo Object (not just users)
.containsObject checks for a null or empty array
Adds FeedManager#getFeedPostsForKey
Adds Post#findByIds
Adds EventsMonitor and ActivityManager

Events are tracked by EventsMonitor.
ActivityManager is how we query our public data collected by EventsMonitor.
These two modules must be separate because Mongoose Models create a circular dependency.

* Stores a post to a feed when a user relays a post.