Org-Specific, User-Specific PMSS

In the past work has been done to develop cascading PMSS modes which allow us to source settings from multiple locations. Now we will need to make those settings cascade by user and org so that an individual user may log in but get different access rules.

No files, tests, or entry points are named. Start by reviewing the existing cascading PMSS modes and determine how settings should be selected by both organization and user; the work is done when an individual user can receive access rules distinct from those of other users or organizations.

Written by the indexing model from the issue text.