Separate the AccountChooser from its model and move options to filters

Create a store for accounts and a filter to only show connected accounts

Update everything to use the new PidginAccountStore and PidginAccountFilterConnected filter

Add a GtkTreeModelFilter for protocols by id

Testing Done:
Compiled and opened most of the dialogs to make sure they're still working the same. Was unable to test gevolution.

Reviewed at https://reviews.imfreedom.org/r/95/