MUS-96 Test refactoring

Changed the drawing tests so that they will be more readable in the
feature (debugging)
MUS-96 Draw refactoring

Split logic from NoteSheetCanvas up into all the drawer classes. Added
a new class NoteSheetDrawer.

Drawing tests will be refactored soon.

Removed some test factory classes because they were not needed.
Refactored NoteSheetCanvas

deleted unuseful code
MUS-96 MediPlayer Fixes

- Added a pause mechanism that stops the media players queue if the user
switches apps
- Added synchronized logic to the media player queue
MUS-96 MediaPlayer Bug Fix

- Added a feature that stops the MediaPlayer on user action (open, save,
play all, redo ...)
- Fixed a bug in which the Play all dialog did not disappear after a
context switch (user presses search button on the phone)
Merge branch 'develop' into MUS-96_DrawPerformance
Merge branch 'develop' into MUS-96_DrawPerformance
Merge pull request #17 from Catrobat/MUS-96_DrawPerformance