Revert "spec: Rename appcategories to categories: The "app" is redundant"
Revert "spec: Rename appcategories to categories: The "app" is redundant"

This reverts commit 2aeee653433fb57a5aa6bcd99a7f0679970b9395.

ximion/appstream,ximion/appstream,ximion/appstream,ximion/appstream