Honour slug uniqueness for menus/resources/resource types

[kierenevans]

Submitting 2 menus with slugs of "foo" places 2 entries in the menu list.

[mackstar]

Yes - this is needs to have a Aspect added - not just for menus but for all resource types.

[mackstar]

You were referring to menus, still need to do this throughout. I have added it to Resources first where it is a priority.

[mackstar]

Still outstanding places are:

• Menus
• Resource types