Move OpenPGP-Keychain to apg
Rename sufficientlysecure.keychain to thialfihar.android.apg
Change some classes from Keychain* to Apg*
Adjust gradle environment

Using libs instead of libraries in preparation of including more
submodules.
Change more things back to APG
Add APG icon again, change theme a bit
Adjust about and changelog texts
Add checkstyle configuration

Run "tools/checkstyle".
Rename "pass phrase" and "armour"
Change "OpenPGP Keychain" to "APG"
Adjust CHANGELOG, remove DESCRIPTION

The README will serve as a description.
Adjust icon, resized via aaresize
Move some classes to pgp
Reorder imports to conform to checkstyle config
Add forgotten break
Adjust variable/method naming to conform to style guide
Conform to style guide
Update copyright span for Thialfihar
Minor style things
Introduce Key/KeyRing wrappers

The goal of these classes is to greatly reduce the needed static helper
classes that work on BouncyCastle key ring and key objects.
Ideally only the pgp package uses BouncyCastle code, the rest of the
app should use this abstraction.

PublicKeyRing and SecretKeyRing exist only for cases where it is vital
that a specific kind of key ring is needed, for instance when it comes
to uploading to a key server, where a secret key ring must never be
used by accident.