How can we phase out the legacy Superset map widgets?

[ethanbienstock]

The Problem

GeoSet users currently see both Map and GeoSet for chart categories when creating a new chart.

This is a bit weird. Also, there's a good chance that new users would immediately be drawn to Map and be annoyed that our functionality is identical to Superset... because they're not using ours.

Thoughts

The simplest fix would be to hide the Map category from the chart selection window. Users could still find the legacy maps by looking through all the chart types.

A better, albeit more involved, solution: completely get rid of the legacy map charts, and ensure that everything that could be done within legacy charts can still be done within the GeoSet charts.

[lhawkman27]

We decided to repurpose the Map category for our GeoSet Layer and GeoSet Map charts. The legacy deck.gl charts were moved under the Legacy category.
MR: #340

The data the Legacy map layers take, all seem to take either an array of lat/lons or a lat and lon coordinate per entry. We already make are data match how Deck.gl renders it's layers like for Path, Scatterplot, Polygons. etc.... So it would be a matter of making our PostGIS data work with the other map layer types. Also, Polygon layers can take data in the form of GeoHash. The World Map leverages a built-in js library DataMaps.js which bundles pre-packaged TopoJSON world geography.