Hello guix!

This patch adds qtpass, one of the GUIs available for password-store. It
should build reproducibly now, and 'guix lint' reports no issues, so
should be ready to go.

Some notes:

- Tests are currently disabled as they seem to need display set. Appears
to be the case for a few qt packages.

- qmake looks for lrelease-qt5/lupdate-qt5 instead of lrelease/lupdate,
and only seems to like the env vars given directly when invoked.
lrelease/lupdate in turn need a variable to find qmake. There's possibly
a more elegant way of doing this.

- Desktop file isn't currently set up; I'll need to look into that.

Comments and advice are very welcome (I'm quite 'green')!

Happy hacking,
Jens M