UC 136 Updating styles and JS for Facebook login modal

The JS and CSS for the UserLogin extension hadn't been touched for a while so there's a bunch of code cleanup and refactoring as well as the addition of a login form on the facebook signup modal. 

Changes to look out for: 
- Added an `htmlTitle` option to the standard UI component modal so we can have a custom html header instead of just a string.
- Updated `UserLoginFacebookForm` JS to `UserSignupFacebookForm` because it was actually handling the signup portion of the modal, even though it's extending the UserLoginAjaxForm. I also added a `UserLoginFacebookForm` to handle the login portion of the facebook modal. 
- In the login modal, the "or" text will only show when `wgUserLanguage` is English. We can add more languages to that as we test them to see that the layout will still look good. There's also different submit button formatting for non-english languages. 

Note: JS and PHP unit tests are passing when I run them in my devbox environment. 
This is pretty trivial, but is there a reason you added UserSignupFacebookForm.js here? It breaks up the UserLogin*.js files. Maybe put it on line 388 instead? Same question for lines 398 and 409.