MUS-34 Removed .*-imports
MUS-34 https://jenkins.catrob.at/view/Musicdroid/job/Musicdroid-custom-branch/21/testReport/
Merge pull request #30 from Catrobat/MUS-34_RefactorSoundMixer

MUS-34 RefactorSoundMixer
Readd unrelated TCs, add DummySoundTrack to simulate adding a track
Readd unrelated TCs, add DummySoundTrack to simulate adding a track
Merged with master
merged