[mediawik.special.changeslist] Remove ugly arrow swapping hack

[mediawik.special.changeslist] Remove ugly arrow swapping hack
* Use CSS and change the background image, instead of displaying 2 <img> tags and hiding one based on the parent element's class
* touches bug 17616 a bit, although it doesn't address the focus issue yet, but does improve the overal structure of this module
* Also speeds up by:
- Outputting less markup
- Having 1 embedded images in the CSS file instead of (N changes)*<img> tags
* jquery.makeCollapsible: