fixes #1298
fixes #919

* change chat states to type=chat and chat markers to type=chat
* use same type as requesting stanza for delivery receipts (which should make them type=chat most of the time)

Can re-enable it via Config.java setting

We introduce a new trust state: INACTIVE. This state is intended for
old keys that have been removed.

When a TRUSTED device is removed from the PEP devicelist, it's status
will be set to INACTIVE. INACTIVE keys are shown in the UI as greyed
out, non-interactible key rows. Messages are not encrypted for INACTIVE
devices.

When an INACTIVE device reappears in PEP, or a message is received from
an INACTIVE device, it is set back to trusted.

fixed #1263
fixed #1260
fixed #1293

Why, oh God, why?! #thanksjamesgosling

This also ensures that the IV is generated with proper randomness.

If there are no UNDECIDED keys, but none of the contact's keys are
trusted, redirect the user to the TrustKeysActivity

Can now long-press a key to permanently purge it.