Add git revision and build date to the version API call

Currently, the REST API call http://openattic.yourdomain.com/openattic/api/hosts/current returns the following JSON object:

{
    "oa_version": {
        "package": {
            "VERSION": "3.6.0"
        }
    }
}

It would be helpful if in addition to the VERSION field it would also return the STATE, REV and BUILDDATE, if they exist. This makes it easier to determine what exact version of oA is running on the server.