Refactor the init of the webdesktop - part2

[derAndreas]

As already done in issue #2 the init of the webdesktop needs a lot refactoring.
Part1 was do rewrite the user specific styles on the load of the webdesktop.

Part2 is to do the same withe the handling of modules and user actions. This is the chance to push all user permissions on the init of webdesktop from the backend to the frontend (maybe configurable) to that the developer of modules can check on the frontend if a user is a allowed to perform some action and change the frontend ui.
As an example: if the user is not allowed to change the background, the "save" button should be disabled or replaced by some informational text.

This refactor is not so big as the user style refactoring, but quite interesting.