Access token invalidation leaves Quaternion in a stalemate

[KitsuneRal]

The current behaviour is that the next sync fails with an error window that proposes an escape path through logout (not bad already) but trying to actually logout ends up with another "Invalid access token" error, with the list of rooms staying intact. The access token gets deleted though; so on the next run Quaternion would ask for login credentials instead of failing again.

What should be: upon receiving M_UNKNOWN_TOKEN, Quaternion should cleanup the interface as if this connection wasn't there and show the login window with all data except password prefilled.

When the library supports it, internally the connection might not even be deleted; rather, a way to update the access token is provided so that the next sync could go on as if nothing happened (with the previous batch token and all the rooms etc. being there). This would make re-logging-in as painless as possible.

[KitsuneRal]

In the light of recent access token invalidations this becomes pretty urgent.

[KitsuneRal]

Turns out the more or less reasonable way out of this is already in Quaternion but is not taken due to a bug in the library.

[KitsuneRal]

This is fixed by the commits above.