Fixes #497

Otherwise we don't include it in the stanza.
So if an error occurs, remove the bookmark again.

So that the chatboxes get closed/removed.

Also, don't render the login form when we're just reconnecting.

after 10 seconds.

Fixes #1172

updates #497

When receiving a PreKeySignalMessage, then a prekey has been chosen and
should now be removed from the list of available prekeys in the bundle,
so that a different device doesn't choose it as well.

AFAICT, libsignal removes the prekey, so it's then up to us to
regenerate it and republish our bundle.

updates #497

Before these changes, prekeys were stored in two places, one place that
converse-omemo accessed and one that libsignal accessed and when
libsignal deleted a prekey the other store wasn't updated.

Now we let the methods called by libsignal store/remove prekeys (and the
signed_prekey) in the same place as used by the code in converse-omemo.

updates #497