Add keywords to the .desktop file

As per https://wiki.gnome.org/Initiatives/GnomeGoals/DesktopFileKeywords
Add missing semicolon to the .desktop file

Keywords spec requires the semicolon
Allow desktop file keywords to be translated

From the docs: "the preceding underscore in "_Keywords" to inform intltool that this field should be extracted, and its translations merged back into the .desktop.in file."

Also tried to group the meta better