https://github.com/azavea/OpenTreeMap-cloud/blob/master/opentreemap/treemap/models.py#L107

We have a convenient method on User, which is _not_ Authorizable for getting Field Permissions. This would be the only hangup, but it's not a problem, really, because it still works within the system of Authorizables. Instead of _using_ authorizables (via the mixin), it is _used by_ authorizable, so it is not inheriting the mixin.

I think that since we're already importing stuff from audit.py, we can just add FieldPermissions to the import list and just adjust the reference on User. It does a decent job of preserving the abstraction. treemap.models imports features from treemap.audit, but not hte other way around. What do you think?