pidgin/pidgin

Make the CredentialManager the only thing in charge of its preferences.

Testing Done:
Started pidgin3 with an empty config directory, verified the notify dialog didn't pop up. Set the preference and exited a few times to make sure everything was working properly.

Reviewed at https://reviews.imfreedom.org/r/1079/
[Desktop Entry]
Name=Pidgin 3
GenericName=Internet Messenger
Comment=Chat over IM. Supports AIM, Google Talk, Jabber/XMPP, and more
Exec=pidgin3 %U
Icon=im.pidgin.Pidgin3
StartupNotify=true
Terminal=false
Type=Application
Categories=Network;InstantMessaging;
MimeType=x-scheme-handler/gg;x-scheme-handler/irc;x-scheme-handler/sip;x-scheme-handler/xmpp;
@USES_MM_CHAT_SECTION@