Add a "push" strategy

[lukemelia]

create triggers a save on the record; build creates the record and leaves it in an uncommitted state. It would be nice to have push, which adds the record to the store in a committed state without going through save in the test.

Thoughts?

[teddyzeenny]

+1 this should be pretty straightforward to do after the ED refactor.

[teddyzeenny]

Something like

Factory.push = function(store, type, props) { 
  return store.push(type, Factory.attr(store, type, props)); 
}

[lukemelia]

yeppers. Looks good.