removed unused files
 * ScriptTabActivity has been replaced by ScriptActivity
add method to enter SoundFragment in ScriptActivity
 * needed for testing
refactored SoundFragmentTest
 * start from MainMenuActivity
mute media stream before playing sound
change SoundActivityTest to ScriptActivityTest
The test was originally designed to test the SoundActivity, but should
now test the ScriptActivity, which holds the fragments (scripts,
costumes, sounds). So it kind of replaces the former ScriptTabActivity.
delete test for ScriptTabActivity
 * not needed anymore