[Engine-Twitter] Simplify TwitterProtocolManager.SortTimeline()
[Engine-Twitter] Implemented "timeline" command

This command can also receive more than one user (separated by commas),
in the same way you can join many IRC channels at the same time, but
with the added feature that the timelines will be joined in just one
groupchat window.
[Engine-Twitter] Fixed ArgumentNullException regression for sent tweets
Merge pull request #132 from knocte/timeline-command
Merge pull request #133 from knocte/master
[Engine] Subscribe to protocolManager.Connected event earlier

It could happen that protocolManager.Connect() function is completely
synchronous, which would mean that the Connected event would be raised
before Session.Connect() method has subscribed to it.
[Engine-Twitter] Fire the Connected event

The twitter backend was not firing the Connected event, which meant
that the "On Connect Commands" were not being executed.