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. 
I'm actually going to leave it for now. This whole function is setting values via magic method, so updating it everywhere would make it so much more verbose, I'm not sure it's worth it. Now that I've looked at it more closely, I think it could use some refactoring to handle fewer use cases in one function. For instance, if the conditional results in the modal use case, we should probably just forward to the modal method, as opposed to getting the `toString` value of the controller output. 

Let's just say this is a candidate for refactor and not open a can of worms now if that's okay.