Merge pull request #204 from csmith/master

Give the BackBuffer an EventFormatter.
Add back buffer entries based on events.

Any formattable DisplayableEvent received on a frame container's
event bus is now automatically added to the IRC Document.

Current problems:
  1) Every time this happens the old path still executes, so you
     end up with two lines
  2) Every event on a channel's event bus gets passed to the
     server's, so the lines appear there as well.