Make sure that permissions in session are always up to date. Fix test
that was failing due to new uniqueness constraint enforcement.
Timestamp of most recent role modification must be placed outside of the
permissions dictionary. Permissions dictionary is currently serialized
to json and passed to the client, and serialization of the Datetime
object fails.
Merge pull request #118 from reciprocity/feature/fix_permissions_session_update

Changes to make sure that permissions are up to date on every request. This is