Support Geopandas >= 0.14.3

[atmorling]

EcoDataFrame wraps GeoDataFrame, and assumes that when we call Geopandas/Pandas methods on EcoDataFrame objects that an EcoDataFrame is returned.

0.14.3 breaks that assumption in a few places, with internal methods that are marked @final meaning we can't wrap them on our side.

Because of that, 'supporting' 0.14.3 will probably mean updating our notebooks/documentation and tests to capture scenarios where a user will have convert back to an EcoDataFrame after certain operations

[atmorling]

After a chat with @cisaacstern, an infinitely better way to do this is to rework our Base classes as dataframe accessors

This puts some pressure on getting #108 completed, so will raise the priority there.