Refactor to move most of Hydra::AccessControls::Permissions into Hydra::Datastream::RightsMetadata and DRY up access exceptions
Refactor access/visibility adding limited visibility to Hydra override
Get rid of limited access level; move user/group exceptions to read_users/read_groups
Switch from imputed (virtual_groups) login logic to explicit (full_login?) logic
Move hidden and virtual group tests to concern specs
Switch to visibility from access
Use mbklein's full_login method to determine shareability