Engine: reverting the removal of UserModel threadsession

This commit is reverting the change that removed the
UserModel from threadsession.  This was need to
support setting the pulp config.  We plan to revisit this
to find a better alternative.
Engine: content views: updates support org or all-org context

This commit has a few changes to support the fact that
a user may be logged in either within an org or without
an org.