General: Content Permissions -- Users can now only view their own content, they can't see other user's structures and plans

This seems like an important set of permissions.

We don't want users to be able to view other user's data (structures and plans), as that could lead to scenarios we want to avoid.  This would reveal who else has accounts, and what locations they are interested in, as well as other things.

At the moment, Plans and Structures are only viewable by those who create them (except for administrators).