implement POST /v2/groups, DELETE /v2/groups/{groupId} and GET /v2/groups/{groupId}

add models for docker container

modify container information for docker containers

implement deployments APIs

implement toString function in Deployment class and add cancelDeploymentAndRollback API

add error decoder. exception throws from this commit when responses http error from marathon

remove commented code
Merge pull request #4 from blurblah/master

Implementation some APIs of the Marathon and error decoder