fixes #903

- This ensures that gstreamer bus operations work
on macOS and windows, such as enumerating devices.

Allows you to zoom and pan now.

relates to #647

This adds a man page which lists command line options, key bindings and
commands. A new CMake option `MAN` is added, enabled by default on
`UNIX` but not `APPLE`.

The man pages are generated with either `a2x` (from asciidoc) or
`asciidoctor`. If both are not found, a fatal error is signaled.

See also:
https://stackoverflow.com/questions/1394910/how-to-tame-the-windows-headers-useful-defines

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

Add support for listing devices that do not support encryption, add support for logging out devices.

Ticks off another box in #23!

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.