Adds a hasBeenFetched property to resources and collections

This property will be useful to check if something has ever been
fetched, regardless of whether it is expired right now.

It is intended to replace checks that poke at the actual data to
determine if something has been fetched and is ready for use, while
side-stepping the transient nature of isFetched.
Using getPath
Merge pull request #96 from zendesk/shajith/has-been-fetched

Adds a hasBeenFetched property to resources and collections