Contributor add collection shouldn't show on admin page

A Contributor can browse public collections, but not add to them. However, on the admin page (in 1.5.1 anyhow), there's a link for a Contributor to add a collection. It goes to a 403 error, but there should be a catch to prevent that link from showing up from that type of account in the first place. It's not a huge issue, obviously, but it could probably be easily fixed.

In a similar vein, I noticed that a non-superuser can approve/disapprove anyone's comments, so that's more of a problem!

Also, I'm pretty sure that deleting an item's tag or tags deletes it from a collection.