(And shrug losing arms in replies)

The event seems to be very expensive on certain platform theme plugins.

Fixes #1639

See https://bugreports.qt.io/browse/QTBUG-110446

This is a bit hacky, because we open a window to actually get a valid
activation token, but...

Before we only did that, when we basically didn't have the key yet. But
since we usually get sent a RoomKey when a new message is sent after we
sign in, we were discarding, that those messages should usually now be
trusted.

fixes #1590

Not just when any setting is modified...

fixes #1563

fixes #1560

fixes #1561