Resolve batch after related fields have resolved

Previously, the batch promised was resolved before all of its associated
models had been loaded. This delays the resolve until everything has been
populated.

@jofomah, could you look over this one to see if I've missed anything? It
should also fix the inventory list "table repopulating" bug we noticed a while
ago.

See: https://www.flowdock.com/app/ehealth-africa/lomis/inbox/46825