pidgin/pidgin

Migrate gg, novel, null, sametime, silc, and zephyr to using G_DECLARE_FINAL_TYPE for their protocol objects

Testing Done:
Compile only.

Reviewed at https://reviews.imfreedom.org/r/620/
[Desktop Entry]
Name=Pidgin
GenericName=Internet Messenger
Comment=Chat over IM. Supports Jabber/XMPP, and more
Exec=purple3-url-handler %u
TryExec=purple3-url-handler
Icon=pidgin
StartupNotify=false
Terminal=false
NoDisplay=true
Type=Application
Categories=Network;InstantMessaging;RemoteAccess;ConsoleOnly;
MimeType=x-scheme-handler/gg;x-scheme-handler/irc;x-scheme-handler/sip;x-scheme-handler/xmpp;
@USES_MM_CHAT_SECTION@