Add link to user manual to Help menu

Yes, we could try and bundle the user manual with the executables and open
a local copy of it - but this seemed much easier and safer to do. It does,
of course, add another string...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Update PO files. AGAIN.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Update German and Swiss-German translations

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>