Update to datastore 0.6.0

[bedeoverend]

Updates to datastore 0.6.0.

Changes:

• [x] Handle get / find returning flat objects rather than of the form { key, data }
• [x] Fetch keys using datastore.KEY symbol on retrieved entities, but at entity.key on creating entities
• [x] Utilise built in promises

Paves the way for using forked 0.6.0 which supports deep exclusions of property indexing