Blacklist mate-*

We only want to show Applications in gnome-software, and Mate settings panels
don't really qualify as applications.
Furthermore, they usually have the same icon and description as the
gnome equivilients, which might make things confusing for users

Since mate settings panels do not have a special category like gnome or
Cinnamon have (for example X-GNOME-Settings-Panel), we have to blacklist
mate-*, and hope that this rule doesn't blacklist too many actual applications.