Doesn't access database directly anymore but goes through AxolotlService
now to obtain list of fingerprints associated with an Account/Contact.
This should prevent orphaned keys littering the UI which previously
couldn't be removed through the Clear Devices function.
Together with 1c79982da84964c1d81179a0927d9cd1eadf53de this fixes#1393
Slider used to skip back on drag-and-drop action. The switch doesn't
trigger explicit whole UI refreshes anymore, it now directly adjusts the
"done" button's locked status.
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.
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.
If the contact (or the own account) has keys that have UNDECIDED trust,
we now drop the user into the new TrustKeysActivity, where they have to
decide for each new key whether it should be TRUSTED or UNTRUSTED.
