This is still a bit flaky around when to remove a mention, but it should
work in most cases. Might add a toggle in the future to disable these
though.

Looks a bit better and works around some height weirdness on my systems.

fixes #1661

Fixes #1125

A new window could have the same `QWindow *` value as an already free'ed window,
so using a `QSet<QWindow *>` with potentially free'ed windows might not be reliable.
Use dynamic properties instead.

Co-authored-by: DeepBlueV7.X <nicolas.werner@hotmail.de>

(And shrug losing arms in replies)

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

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

Fixes #1639

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