Improving module loading code in cpanel layout

I did two things
* Removed unneeded code mainly related to `$params`. That was probably some leftover code from long ago.
* Check if there is a module published on `icon` position. If there is no module published on this position, don't show blank space and let the other modules use this place instead.

Tracker:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32203