1) Move all the crypto classes from securesms.crypto.
2) Move all the crypto storage from securesms.database.keys
3) Replace the old imported BC code with spongycastle.
The best-effort memory cleaning logic for MasterSecrets
is no longer accurate, since they are being passed through
both Binder calls as well as Intents, blurring whether an
activity is using a MasterSecret which is a reference to
shared memory in the KeyCachingService or not.
