UC-145 Add FB disconnect button to prefs

RFCR @lizlux 

https://wikia-inc.atlassian.net/browse/UC-145
Line 49 is a bit tricky and line 50 is a bit hacky. Blindly removing all class is tricky b/c what if someone else puts a class name on this element at some time in the future. Adding back in the known class names is hacky b/c it's basically hard coded. 

An alternative would be to pass a function to `removeClass` [docs](http://api.jquery.com/removeclass/) that can perform a simple regex on the current class names and remove one if it passes.