RecyclerView

It was a lot more work than expected, but I almost finished the RecyclerView and it looks and behaves like the old view! The memory footprint looks better than ever!! Since the RecyclerView never has all adapter items as a child, I had to move the progress bar into SecrecyFile to always get a reference to that.
I also cleaned up the weird ViewNHolder concept.

Besides the RecyclerView there was another bug which consumed memory. The adapters where never unregistered from the EventBus. Thus there was always a reference to them even when you left the vault and so the garbage collector could never clean them.

I didn't clean up this PR and added all just in one big commit. I'll clean up later and then it could be merged.

I think when this is finished and possible bugs are fixed, we can release the "faster-than-ever--more-secure-than-ever" alpha. (Although I would really like to have a second person checking the new encryption stuff)

Fixes #57 
Fixes #16 
Fixes #5