Currently if you have 5 collections, you'll get 5 items:

• Add to collection "My Collection #1"
• Add to collection "My Collection #2"
• Add to collection "My Collection #3"
• Add to collection "My Collection #4"
• Add to collection "My Collection #5"

We should instead have only one link "Add to collection..." that opens an ajax dialog.
In this dialog you should be able to:

• add the release in multiple collections in one go
• create a new collection