Create a new PurpleProtocolManager

* Created new PurpleProtocolManager object.
* Updated the existing purple_protocols_* api to call the new api in the
manager.

Testing Done:
* Ran unit tests
* Ran libpurple-doc
* Ran pidgin locally with bonjour, xmpp, and irc.

Bugs closed: PIDGIN-17462

Reviewed at https://reviews.imfreedom.org/r/437/