Renamed MD5 method and added one which returns byte[] instead of BigInteger

Signed-off-by: Matthias Stevens <matthias.stevens@gmail.com>
- Moved getImageFile() and getSoundFile() from Project to FileStorageProvider
- changed audio feedback related stuff
DOES NOT COMPILE

Signed-off-by: Matthias Stevens <matthias.stevens@gmail.com>
Half-fixed issues left over from refactor so this can be merged into
audiofeedback branch.
Merge branch 'temp_for_ben' into ben_audiofeedback

Conflicts:
	CollectorAndroid/src/uk/ac/ucl/excites/sapelli/collector/ui/AndroidControlsUI.java
	CollectorAndroid/src/uk/ac/ucl/excites/sapelli/collector/ui/fields/AndroidChoiceUI.java
	Library/src/uk/ac/ucl/excites/sapelli/collector/model/fields/ChoiceField.java
Progress on hooking up audio feedback, but getting NPEs when parsing
project.