Experiments with building mousepad with meson

[flo.xfce at gmx-topmail.de]

The branch now installs properly and I removed one of the files I
additionally created, but not the second desktop file template (see my
other post on this mailing list about replacing intltool with gettext).
I didn't start this branch because I was unhappy with make's performance
but rather with autogen/autoconf. It unsatisfying if the configure step
takes longer than the actual compilation itself. (This doesn't mean that
autotools are too slow to be used).
And I can only repeat myself: This work is not intended to be a
replacement of autotools. It works fine. I agree, working on the build
system or other surroundings is probably not as important as work on the
code itself. So building with meson should only be a second choice
offered to the user/developer.