Fixed issues: #252(Priority-Critical) and #246(Priority-High)

* Fixed #252 (Changing/Setting user variables does not work)
* Fixed #246 (Confusion where to create variables)

Complete Jenkins testruns:
* http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/777/
* http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/778/