Add a delay to all destructions and move the call dialog stuff up a
level, so that we don't destroy the component when destroying the parent
dialog.

fixes #984

fixes #878

See #469

It seems that you need to manually destroy created objects... Great...

fixes #898

So we don't have to retranslate.

Allows you to zoom and pan now.

relates to #647

fixes #683
relates to #571

This was a bit of a journey:
https://github.com/matrix-org/matrix-doc/pull/3471
But it should work now and we now use the UIAHandler everywhere.

fixes #670

This ports the leave room dialog to QML, everywhere. There are now no differences between the various leave dialogs.

Showing the bootstrap state and showing there are unverified devices is
still missing.

We explicitly set a parent. We can't assign to
ApplicationWindow.transientParent though, only to
Window.transientParent, so we just call setTransientParent in C++.

There are probably a few things wrong with this, but I'm going to call it good enough for an initial commit

Also fix a lot of warnings.