Bound the ThreadLocalRequestContext module, which makes the CurrentUser
available in the Global module. Removed any binding in the scopes that
provided the CurrentUser. Updated all of the scopes to propagate the
RequestContext. The PerThreadRequestScope.Propagator allows scoping
callables to enter a request context.
Change-Id: Idf682ed1d7485cf8c9cdd22cd89bfe1ad5296880