change RemoteEntityAPIDefaultController::load() to load entities remotely in bulk

I've added a remote_entity_load_multiple() to the resource class (and also the connection module that I use).

The next step is to change the entity controller's load() to use this. Currently, it examines each entity in turn and loads it from remote if it's stale. Instead, we should examine each entity, build an array of stale entities, then load those in bulk -- and let the resource class take care of determining whether the connection supports a bulk load.

(I'd have done this as part of what I've done so far, but I'm rushing for a deadline...)