pidgin/pidgin

Add PurpleCredentialProvider as the first piece to replace the existing keyring api.

Testing Done:
Added some new unit tests and made sure they passs.

Reviewed at https://reviews.imfreedom.org/r/144/
subdir('bonjour')
subdir('facebook')
subdir('gg')
subdir('irc')
subdir('jabber')
subdir('novell')
subdir('null')
subdir('sametime')
subdir('silc')
subdir('simple')
subdir('zephyr')