White splash screen fix & fix for parallel execution of when scripts

Concerning #88 and #213 .

* White splash screen does not appear any more, but stays as default background.
* Now when scripts are executed parallel. (with a parallel action)

Jenkins Testrun:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/683/
testNestedRepeatBrick:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-jUnit-test/62/