Adding support for Mapbox with Polygon

[prasar-ashutosh]

Mapbox Polygon support

This pull request is an attempt to implement the feature: #2675

Background
We are using superset with Druid in our project at Dataspark, Singtel, Singapore. We needed Mapbox with Polygon support in our project. So we have attempted to solve this problem using react-map-gl , deck.gl and d3. The new visualization is called "Mapbox with Polygon".

Usage

• Create a new slice
• Select the datasource as : "birth_france_by_region"
• Select the visualization type : Mapbox with Polygon and click on "create a new Slice"
  
• In the Query section , select the DEPT_ID under "Codes of region/province/department" and select a metric.
• Click on Query. Zoom in/out to adjust if needed. hover around the map to see the details.

Features
The visualisation supports the following filters/selectors

1. Time
   

2. Query
   

3. Options

   • GeoJosn : select the geojson layer
   • RGB color sheme : select the Color scheme
   • Map Style : Select the map style
   

4. Viewport
   

5. SQL
   

6. Filters
   

[mistercrunch]

We already have support for DeckGL polygons here:
superset/assets/visualizations/deckgl/layers/polygon.jsx

Also many other layer types and multi-layers charts! We haven't released it yet, coming in the next release.

[mistercrunch]

Thanks for the PR regardless, looking forward to future collaborations.