This command finalizes support for dynamic message loading. The behavior is as follows:
When a user selects a channel for the first time, an "initial load" of messages will happen.
When the user is scrolled all the way to the bottom of the message view,
the store will continuously remove old messages to save memory.
Scrolling all the way to the top loads more messages.
This commit simplifies the store code by removing the _init method, and instead initializing
everything on instantiation. This leads to not missing events and less complexity.
