Upgrade to alpha release of Datomisca (v0.7 branch)

This pull request upgrades the Datomisca Autosource to the v0.7 branch of Datomisca.

Datomisca `0.7-alpha-3` and Play-Datomisca `0.7-alpha-1`, should be considered stable pre-releases, rather than snapshots—and the code is fairly stable as well.

@mandubian, I’ve published this internally as `2.1-8f27ea594f`. I’ll leave it up to you to bump version numbers.