Deprecate folium module in favor of GeoPandas explore

[gboeing]

Resolves #802 and #935.

• Deprecates the folium module in favor of using the more powerful and flexible GeoPandas.GeoDataFrame.explore directly. GeoPandas docs. See also.
• Adds a new route_to_gdf helper function to the utils_graph module to make it easy to explore a route
• Deprecates the get_route_edge_attributes function as it becomes redundant with the superior route_to_gdf

See gboeing/osmnx-examples#64 for demonstration code in the examples repo. You can:

• interactively explore nodes, edges, or both together, optionally colored by attribute values
• interactively explore a route
• interactively explore building footprints, transit, amenities, etc

[codecov]

Codecov Report

Merging #957 (26d9d54) into main (1eab896) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #957   +/-   ##
=======================================
  Coverage   97.87%   97.87%           
=======================================
  Files          24       24           
  Lines        2348     2357    +9     
=======================================
+ Hits         2298     2307    +9     
  Misses         50       50           

Impacted Files	Coverage Δ
osmnx/folium.py	100.00% <100.00%> (ø)
osmnx/utils_graph.py	97.64% <100.00%> (+0.08%)	⬆️

[gboeing]

@PyMap I believe this covers all the uses you had considered in #802. See gboeing/osmnx-examples#64 for demonstrations.