PassphraseRequiredMixin might check for a bound service at a time where
the bind has been requested but the service connection has not been
established yet, and therefore fail to call unbindService, leading to a
leaked service connection. This fixes#1518.
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.
1) Consolidate all of the KeyCachingService interaction into a single
mixin. Activities extend delegates which call through to the mixin.
2) Switch Activity increment/decrement triggers from onStop to onPause
in order to account for some screen locks that don't stop activities.
