Can complete tree stewardship process when permission prevents it

[dboyer]

Tested on 323 dev ipa.

1. Added a tree and saw correct permissions
2. Selected add new stewardship entry and saw option to select tree and planting site when public users should only be able to add planting site
3. Added a planting site stewardship. Completed process successfully and it appeared on the tree detail page.
4. Added a tree stewardship activity and could click Save. Stewardship entry appeared on the tree detail page.
5. Exited the tree and then reentered the detail page. Planting site stewardship was visible but tree stewardship was not.