Group: add version
GroupRepository: basic persistence
Merge branch 'wip-deployment-features' of https://github.com/mesosphere/marathon into wip-deployment-features

# By Dario Rexin
# Via Dario Rexin
* 'wip-deployment-features' of https://github.com/mesosphere/marathon:
  small changes

Conflicts:
	src/main/scala/mesosphere/marathon/api/v2/Group.scala