Made this actually work with more modern MediaWikis.

Lots of changes here, some of which I've probably already forgotten about.
Here's a listing of the changes I actually can remember:
* CSS fixes
* moved AjaxLogin HTML code to a new file
* moved hooked methods into their own file
* stylized jqModal
** jqModal.r16.js is revision 16 of jqModal; I tested that with AjaxLogin
and it mostly broke everything; if and when jqModal is to be updated,
AjaxLogin's JS code will also need changes
* proper ResourceLoader support

Change-Id: Iff4f2296cf119fd2b8c38255e55ec043e26cb92a