Added DeckGL.Polygon Layer w/ JS controls (#4227)

* Working polygon layer for deckGL

* add js controls

* add thumbnail

* better description

* refactor to leverage line_column controls

* templates: open code and documentation on a new tab (#4217)

As they are external resources.

* Fix tutorial doesn't match the current interface #4138 (#4215)

* [bugfix] markup and iframe viz raise 'Empty query' (#4225)

closes https://github.com/apache/incubator-superset/issues/4222

Related to: https://github.com/apache/incubator-superset/pull/4016

* [bugfix] time_pivot entry got missing in merge conflict (#4221)

PR here https://github.com/apache/incubator-superset/pull/3518 missed a
line of code while merging conflicts with time_pivot viz

* Improve deck.gl GeoJSON visualization (#4220)

* Improve geoJSON

* Addressing comments

* lint

* refactor to leverage line_column controls

* refactor to use DeckPathViz

* oops

superset/data/__init__.py

@@ -1552,6 +1552,36 @@ def load_paris_iris_geojson():
     tbl.fetch_metadata()
 
 
+def load_sf_population_polygons():
+    tbl_name = 'sf_population_polygons'
+
+    with gzip.open(os.path.join(DATA_FOLDER, 'sf_population.json.gz')) as f:
+        df = pd.read_json(f)
+        df['contour'] = df.contour.map(json.dumps)
+
+    df.to_sql(
+        tbl_name,
+        db.engine,
+        if_exists='replace',
+        chunksize=500,
+        dtype={
+            'zipcode': BigInteger,
+            'population': BigInteger,
+            'contour': Text,
+            'area': BigInteger,
+        },
+        index=False)
+    print("Creating table {} reference".format(tbl_name))
+    tbl = db.session.query(TBL).filter_by(table_name=tbl_name).first()
+    if not tbl:
+        tbl = TBL(table_name=tbl_name)
+    tbl.description = "Population density of San Francisco"
+    tbl.database = get_or_create_main_db()
+    db.session.merge(tbl)
+    db.session.commit()
+    tbl.fetch_metadata()
+
+
 def load_bart_lines():
     tbl_name = 'bart_lines'
     with gzip.open(os.path.join(DATA_FOLDER, 'bart-lines.json.gz')) as f: