don't keep the ViewObserver as it may not be alive when we need to remove our view
(otherwise it crashes when the PhotoView is in a Fragment in a ViewPager and the page is no longer kept)
no need for the dummy files to compile
unset listeners on cleanup to avoid events coming asynchronously
@Override is always a good indication in the code
use LogManager so logs can be redirected if needed
avoid doing cleanup twice, fixes a crash when null mImageView is called
Merge pull request #37 from levelup/lu_dev

Fixes an issue when PhotoView is in a ViewPager