update(GeoSpatialCollection): add support for GeoDataFrame objects

[jlarsen-usgs]

• update test_geospatial_util.py to include GeoDataFrame tests
• add geopandas as optional dependency

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (97da396) 73.0% compared to head (1d08926) 73.0%.
Report is 4 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2063     +/-   ##
=========================================
  Coverage     73.0%   73.0%             
=========================================
  Files          259     259             
  Lines        57887   59320   +1433     
=========================================
+ Hits         42263   43327   +1064     
- Misses       15624   15993    +369     

Files	Coverage Δ
flopy/discretization/structuredgrid.py	47.6% <88.8%> (+0.4%)	⬆️
flopy/discretization/unstructuredgrid.py	85.4% <88.8%> (+<0.1%)	⬆️
flopy/discretization/vertexgrid.py	83.5% <88.8%> (+0.1%)	⬆️
flopy/discretization/grid.py	76.0% <77.7%> (-0.2%)	⬇️
flopy/utils/triangle.py	65.8% <60.0%> (+<0.1%)	⬆️
flopy/utils/geospatial_utils.py	92.8% <84.2%> (-1.0%)	⬇️

... and 73 files with indirect coverage changes