XmppAxolotlMessage is now entirely responsible for handling encryption
and decryption of messages, only leveraging XmppAxolotlSession as a
packing/unpacking primitive for payload keys.
Removed pseudo-dead session generation code step from prepareMessage
function, as sessions have been created by invoking the
TrustKeysActivity for a while now.
Added prepareKeyTransportMessage function, which creates a message with
no payload. The key that is packed into the header keyElements can then
be used for other purposes (e.g. encrypted file transfer).
Messages sent from another device of the own account are now explicitly
tagged as carboned message. The session detection logic now uses this
tag to find "session borders".
Plaintext messages that were received while in an encrypted session are
now colored red. We define "in an encrypted session" if a) the last
message sent by our own device before the message under consideration
(or any message received between then and now) was encrypted AND b) the
next message will be sent encrypted or the next message sent after the
one under consideration was sent encrypted
Moves SQLiteAxolotlStore and XmppAxolotlSession into proper classes.
IdentityKeys trust statuses are now cached in an LruCache to prevent
hammering the database when rendering the UI.
* 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)
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.
