Fix for Issue#342

Objectvariables (~Spritevariables) now are correctly remembered after exiting the stage.

Fix #342 (related fix for issue #269 already in masterbranch)

Test (single UI): http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/798/ (finished)
Custom-branch test: 
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/1120/
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/1161/
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/1176/