fixed following issues:
* Icons in Editing-Mode in Dock and Blocks
* Fixed z-index Issue concerning problem with yui3 elements when trying
to add an activity or ressource
* Removed Shadow of Dock
* Removed Background Image in Course and moved everything 20 pixel to
the left (increased course content space)
* Inverted colors of course content elements (grey<->white)
* added CSS3 shadow for course content elements
* removed not needed code