Fix some issues with the protocol chooser and clean up its usage in GtkAccount

Added `PidginProtocolStore` and `PidginProtocolChooser` to the Glade catalog.
Updated the template for `PidginProtocolChooser` to use a `GtkTreeModelSort` to sort the list of protocols.
Ported the existing `purple_protocols_*` API use to `pidgin_protocol_manager_*`

Testing Done:
Verified the new account dialog shows up properly with the protocol chooser sorted.
Verified that editing an account had the proper protocol selected.
Verified that changing a protocol on an existing account worked.

Bugs closed: PIDGIN-17471, PIDGIN-17491, PIDGIN-17495

Reviewed at https://reviews.imfreedom.org/r/533/