Add a connection parameter to the PurpleProtocolActions.get_menu virtual function

This is necessary so that protocols can dynamically add menu items for specific
accounts. This could be something like adding administrator actions after the
protocol has determined that you're an administrator for example.

Testing Done:
Connected an xmpp, ircv3, and demo account and verified all of their actions were displayed properly.

Reviewed at https://reviews.imfreedom.org/r/2172/