Remove acl9, replace with SimpleRole

acl9 gem is a little bit opaque, had (at least one) rails 4.1.x incompatibility, and its tests are written in a convluted style with Test::Unit. Since our needs are simple (see what I did there?), rewrite, as SimpleRole, only implementing the methods that we use, and hardcoding (would be simple to generalize, but there is no need) class names for associations.
curious to hear more of your thoughts here. should we remove the explicit owner association here and just use the :owner role? should i remove the owner_type/owner_id columns, but preserver the relationship by using the roles/roles_users table to make the same join? or should i keep the redundant functionality?