tracking: Implement Record Links & Meta (rfc#332)

[runspired]

We would still like to implement emberjs/rfcs#332

This entails:

• adding methods for retrieving resource level links and meta to the cache API
• adding links/meta to the response of Cache.peek
• adding links/meta support to the notifications API
• adding links & meta properties to Model that are overridable by attr fields for users that have existing fields with name conflicts
• exposing the links & meta vis Snapshot and Reference APIs

At this time, resource links would not be used during any automated fetch behavior. We do not wish to change existing adapter mechanics, and users of the request API would just need to pass the link into the request (vs anything automated). SchemaModel might use these links for save/reload behaviors, but Model will not change any existing behaviors.