Fixing some bugs with cookbook ownership and collaborators

:construction: 

This is for this card: https://trello.com/c/UN4xLTmj/4-cookbook-maintainers-can-add-and-remove-cookbook-contributors-from-the-cookbook-show-view

There are 2 items left in the checklist, and they need to be tackled by someone with more design savvy than I have.