Generate JSON

Generate JSON data so that tools can easily make use of the info
that reviewday generates.

A new reviewday.json file is generated that has data like

  {
    "generated": "2014-01-03 22:22:33",
    "projects": {
      "identity-api": {
        "https://review.openstack.org/#change,62961": {
          "owner": "Dolph Mathews",
          "score": 48,
          "cause": "No link",
          "feedback": {
            "lowest": 1,
            "highest": 1
          },
          "subject": "cleanup query_string documentation"
        }, ... (for each review uri)
      }, ... (for each project)
    }
  }

Change-Id: Idabafdadb3237410fa866c78d429cf46317fb3fe
Merge "Generate JSON"