Integrate with QueryKit

There is a lot of overlapping functionality between KFData and QueryKit since QueryKit is designed to be a smaller set of KFData's. Just providing the KFAttribute and KFObjectManager features. As apart of #65, breaking these components out.

- [x] Move KFAttribute to QueryKit (`QKAttribute`).
- [x] Move KFObjectManager to QueryKit (`QKQuerySet`).

This depends on the work done in https://github.com/kylef/QueryKit/pull/13