Allow admins to update user project preferences

[lcjohnso]

Current behavior: Only project owners are allowed to edit the settings key for a user's project preferences. Example usage: see Python Client documentation here for workflow leveling up (i.e., for Gravity Spy and others).

Desired behavior: Also allow Zooniverse admins to edit the settings key.

Potential Solution: Add a check for admin as an or condition to this statement:
https://github.com/zooniverse/panoptes/blob/24a67c6f4a56492a56e65170fad89ab3bda4c1e0/app/controllers/api/v1/project_preferences_controller.rb#LL25C73-L25C73

[lcjohnso]

Closed by #4218