Add API version to '/management/info' endpoint

[trisberg]

The /management/info endpoint currently has this:

{
  "app": {
    "name": "spring-cloud-dataflow-server-local",
    "description": "Spring Cloud Data Flow Local Server",
    "version": "1.2.0.M1"
  },
  "git": {
    "commit": {
      "time": "2017-02-15T00:06:45.000Z",
      "id": "06674a6"
    },
    "branch": "master"
  }
}

We could add an "api":"version" entry as well, this way the shell can query the compatible version and if it's not deemed compatible post a link to download the shell via the about page at /dashboard/index.html#/about