DECKGL integration - Phase 1 (#3771)

* DECKGL integration

Adding a new set of geospatial visualizations building on top of the
awesome deck.gl library. https://github.com/uber/deck.gl

While the end goal it to expose all types of layers and let users bind
their data to control most props exposed by the deck.gl API, this
PR focusses on a first set of visualizations and props:

* ScatterLayer
* HexagonLayer
* GridLayer
* ScreenGridLayer

* Addressing comments

* lint

* Linting

* Addressing chri's comments

superset/assets/javascripts/modules/colors.js

@@ -142,3 +142,13 @@ export const colorScalerFactory = function (colors, data, accessor, extents) {
   const points = colors.map((col, i) => ext[0] + (i * chunkSize));
   return d3.scale.linear().domain(points).range(colors).clamp(true);
 };
+
+export function hexToRGB(hex, alpha = 255) {
+  if (!hex) {
+    return [0, 0, 0, alpha];
+  }
+  const r = parseInt(hex.slice(1, 3), 16);
+  const g = parseInt(hex.slice(3, 5), 16);
+  const b = parseInt(hex.slice(5, 7), 16);
+  return [r, g, b, alpha];
+}

superset/assets/javascripts/modules/geo.js

@@ -0,0 +1,25 @@
+export const defaultViewport = {
+  longitude: 6.85236157047845,
+  latitude: 31.222656842808707,
+  zoom: 1,
+  bearing: 0,
+  pitch: 0,
+};
+
+const METER_TO_MILE = 1609.34;
+export function unitToRadius(unit, num) {
+  if (unit === 'square_m') {
+    return Math.sqrt(num / Math.PI);
+  } else if (unit === 'radius_m') {
+    return num;
+  } else if (unit === 'radius_km') {
+    return num * 1000;
+  } else if (unit === 'radius_miles') {
+    return num * METER_TO_MILE;
+  } else if (unit === 'square_km') {
+    return Math.sqrt(num / Math.PI) * 1000;
+  } else if (unit === 'square_miles') {
+    return Math.sqrt(num / Math.PI) * METER_TO_MILE;
+  }
+  return null;
+}