More consistent language with similar description strings
Add manpage entry
Add /unignore
Add ignore & decline button in the invite page
Add invite rejection to all ignore methods

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

fixes #1598