problem with filechooser in StartSoundBrick and SwitchtoLookBrick fixed 

testrun on jenkins:
https://jenkins.catrob.at/view/All-Categories/view/Catroid-multi-job/job/Catroid-Multi-Job-Custom-Branch/1544/
one testcase fails, but it for me i doesn't have to do with my changes.

this branch solves following issues on jira:
CAT-955
CAT-967