css framework

Just for discussion, please don't merge yet..

The idea is to move important css classes / tags to its own file. Designers shoudn't worry much about RTL compability or system relevant parts. Currently it's hardcoded in loadTemplate, maybe we should make it a theme parameter $loadCoreCSS = true;

 I've started with the important ones (text-aligns, floats...) but I think we could move other things as well:
- menus
- buttons
- progress bar
- page links
- breadcrumb navi
- help popups
- sticky, locked and other icons..
...

Designers could still use the theme's index.css to overwrite these classes..