Remove GMail accounts

Directly using GMail accounts was a hack that worked for early
Android versions. Currently it isn't usable on most devices, so
it won't be maintained.
Fix DecryptActivity crash
Expect bouncycastle inside the project

Currently left as a symlink, this throws out the hardcoded directory and
is more agnostic about the bouncy castle library.

It might be useful to just include the modified and reduced
bouncy castle sources.
Trivial clean up
Use android-19 as target
Update APG version