CustomFilter mapper fixes

the CustomFilteredListLoader now listens for changes in source bindings (so e.g. if I have a workflow cycle that changes to not current, it's removed from the Workflow's "current_cycle" mapping), and always waits for source bindings to refresh instances (this is important because the CustomFilter, unlike other mappers, uses instances from source bindings instead of stubs -- other bindings can look for the presence of _refresh_stubs_deferred, but just looking for the presence of _refresh_instances_deferred causes a race condition).

CORE-114