Hierarchy between permissions

[mitar]

It would be great to have support for hierarchy between permissions. So that you can have a higher level permission with lower level sub-permissions. So you could then assign the higher level permission, but user would get also all lower level permissions. If more lower level permissions are added to the higher level permissions, those permissions in effect for all users on all object with that higher level permission.

[brianmay]

Going to close this in favor of #23. Can be reopened if we find it is different.