Gray out/make disabled apps insensitive

[cassidyjames]

If an app is disabled by Parental Controls, we could somehow mark that on the Applications menu, i.e. by graying the icon out or badging it somehow. Remember that it's still possible to open the app with administrator privileges, so it can't be completely insensitive.

[danirabbit]

Desaturation seems to be a convention that other platforms are using