Add capability to summarize GridLayout dashboard (for grafana 5.0 or later)

[iori-yja]

The very first introduction for GridLayout dashboard.

% node src/index.js summarize dashboard
Output:
{
  "title": "Monitoring",
  "gridSize": {
    "x": 24,
    "y": 56
  },
  "panelCount": 29,
  "time": {
    "from": "now-12h",
    "to": "now",
    "timezone": ""
  }
}
✔ Showed dashboard General/monitoring summary successfully.

As several issues reported (eg. #129), the GridLayout is the thing that makes wizzy to fail to care recent grafana dashboard. This is the very first concept introduction for this missing capability.

[Sytten]

Thanks a lot for the PR, I will review it during the weekend. Since I still don't have access to the npm package this won't make it into prod, but I am working on it.

[Sytten]

I am sorry I didn't find the time to review it, I am in a rush this month...