changedAttributes and changedRelationships not live.

[aars]

In the current implementation, changes are tracked in objects, which computed properties can not track sufficiently. Computed properties like changedAttributes do not update live, and therefor can not be used for changing state in a template for example.

I think we can resolve this by tracking changes in an array, keep a list of keys that have changed (do not match their previous value).

I will send in a PR next week for this, but wanted to give the chance to discuss this in an issue, since I might have overlooked something that either does allow tracking the dirty state of a Resource, or a reason to not list changed keys in an array.

Cheers.

[aars]

#140