This requires Qt 5.9 (to calculate overshoot).
The default scroll behaviour of list views has far too much inertia.
This should make scrolling feel more like scrolling the other scroll
areas of nheko.

Add file encryption / decryption support

It is a bit of a hack, but it works...

Qml timeline

No idea, why apply visitor doesn't work with temporaries?

Also lays a bit of groundwork for better reply rendering

Thanks to red_sky for the feedback!

This also makes long messages unreadable, because we don't shorten long
usernames anymore. We may eventually want to do that again, but it is
hard with translations and we probably want to shorten the displayname
more, as before this change the message was only ever as long as the
timestamp, which is usually just 5 characters...