Removes disk caching code

Caching is hard and we're not doing a great job of it Since we're not even using the disk cache code, and all of our files are on disk anyway, remove disk caching code and thus some complexity.
Override some more lifecycle methods so we can see when they're happening.
Updates some comments
Move creation of image loader into onResume and display image after copying to media store

Explicity recycle bitmap we create for the media store, since it's full-resolution and we know when we're done with it. This seems to fix (or go a long way toward fixing) #3.
Only put image into media store if it's not already there