Refactored Add Look Dialog

Changed the Add Look Dialog concerning to #404 to "Choose image" and "Draw new Image"

Jenkins Testrun:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/1200/
JUnit only:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test-source-and-jUnit-tests-only/69/
5 times SetLookBrickTest:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/832/console