This change adds a new item to the group configuration: a list of
groups whose members should be included in this one. This makes it
possible to set up a hierarchy of included groups, which can make it
easier to maintain complex access control lists.
To accomplish this, two new database tables were added,
called AccountGroupIncludes and AccountGroupIncludesAudit.
The relevant support code was added around them, largely based on
the existing code for handling indivdual account membership. In
addition, caches for group information were added, paralleling the
caches that already exist for accounts.
Change-Id: Ib6990c17739f28f38bc13961143db7ce79251567
620255aef7