Merge IRCProtocolHandler into IRCAdapter

Summary:
Clearly silly to have a separate handler for this. I also made most of the protocol stuff direct writes so we don't need to ship them through handlers, and made the adapter ignore message it does not understand by default instead of sending them to IRC, and added PASTE "support".

We could still let handlers react to these messages by emitting them all as 'RAWIRC' or similar, but there's currently no need for that so I didn't bother.

Also fix an issue in D4924 with nickpass.

Test Plan: Had bot join IRC, talked to it.

Reviewers: indiefan

Reviewed By: indiefan

CC: aran

Differential Revision: https://secure.phabricator.com/D4925