Support pushing embedded json into fixture adapter

Users can now push json with embedded records via store.pushPayload
while using the fixture adapter.

It supports the following method signatures:
store.pushPayload('user', { id: '1', name: 'john'})
store.pushPayload({
  users: [{ id: '1', name: 'john', project: '1' }],
  projects: [{ id: '1', name: 'ember-data', users: ['1'] }]
})
store.pushPayload('user', {
  users: [{ id: '1', name: 'john', project: '1' }],
  projects: [{ id: '1', name: 'ember-data', users: ['1'] }]
})

Doesn't use serializerFor like the store for non-fixture adapters
So as a side effect:
  typeForRoot not yet supported
  normalize(Links|Payload|Hash) not yet supported
Merge branch 'pushpayload-embedded' into alpha

Conflicts:
	dist/amd/factory-guy.js
	dist/ember-data-factory-guy.js
	dist/ember-data-factory-guy.min.js
	src/store.js
	tests/store_test.js
	vendor/assets/javascripts/ember_data_factory_guy.js