(CE-755) Don't allow disabled accounts to login through FBConnect

Also, provide a hook to allow aborting FBConnect logins.
(CE-755) Disconnect Facebook accounts on account closure
JS-Beautify JS file
Move check for disabled logic to helper method
Move extension enabled check out of method
Merge pull request #3401 from Wikia/CE-755

(CE-755) Disallow login via FBConnect for disabled accounts