desktop: changed translations to msgfmt and xgettext
During the build of the debian package 1.2.0-5 it turned out
that the pspp.appdata.xml file has a wrong structure with
respect to the translations. I did the following things
- renamed pspp.appdata.xml to org.fsf.pspp.metainfo.xml
- added gettext translation support for org.fsf.metainfo.xml
- renamed pspp.desktop to org.fsf.pspp.desktop
- replaced gen-det-desktop.sh based translation with gettext
gettext has now support for translating .desktop and .metainfo.xml
files. I took the naming conventions from the freedesktop and gnome
documentation, i.e. metainfo instead of appdata and the use of
an organization name.