Support for Geopandas Dataframes

[snoopfab]

It would be nice for perspective python api to support geopandas dataframe in conjunction with the perspective-viewer-maps plugin.

We could then use the columns geopandas.array.GeometryDtype to feed geometries to map plugins directly from the Table.

Right now it throws the following exception :
Mixed datasets of numpy.ndarray and lists are not supported.

When viewed with a table plugin the view could show a simple text overview of the geometries like geopandas does :

     pop_est      continent  ...  gdp_md_est                                           geometry
0     920938        Oceania  ...      8374.0  MULTIPOLYGON (((180.00000 -16.06713, 180.00000...
1   53950935         Africa  ...    150600.0  POLYGON ((33.90371 -0.95000, 34.07262 -1.05982...
2     603253         Africa  ...       906.5  POLYGON ((-8.66559 27.65643, -8.66512 27.58948...
3   35623680  North America  ...   1674000.0  MULTIPOLYGON (((-122.84000 49.00000, -122.9742...

4  326625791  North America  ...  18560000.0  MULTIPOLYGON (((-122.84000 49.00000, -120.0000...
5   18556698           Asia  ...    460700.0  POLYGON ((87.35997 49.21498, 86.59878 48.54918...
6   29748859           Asia  ...    202300.0  POLYGON ((55.96819 41.30864, 55.92892 44.99586...
7    6909701        Oceania  ...     28020.0  MULTIPOLYGON (((141.00021 -2.60015, 142.73525 ...
8  260580739           Asia  ...   3028000.0  MULTIPOLYGON (((141.00021 -2.60015, 141.01706 ...
9   44293293  South America  ...    879400.0  MULTIPOLYGON (((-68.63401 -52.63637, -68.25000...

By the way , i think that perspective is a really well written and performant piece of code !