Adding Keywords to .desktop files, following the suggestions in
https://bugs.freedesktop.org/show_bug.cgi?id=47157#c0

Change-Id: Ic2a1428aaa12bc31b0af8488d166f78d5a970a1d
Reviewed-on: https://gerrit.libreoffice.org/490Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>