Add store.push and store.recordFor

store.push is a replacement for store.load. It takes a normalized JSON
structure and optionally uses a serializer to do additional work if one
is available under the type's name.

store.recordFor returns an unpopulated record for the given type and id.
Future calls to `store.push` will move it into the loaded state.
Add debugInfo to DS.Model
Merge pull request #1106 from teddyzeenny/debug-info

Add _debugInfo to DS.Model
Make the data materialized again