add possibility to do contour plots - and plot multiple data sets

[AshleySetter]

No description provided.

[markusrademacher]

for multiple datesets in hexbins:

Either one could append different datasets to each other or one would create a second color palette for the second dataset ... here is an example that might be useful for the implementation seeing that it plots a non-gaussian distribution https://stackoverflow.com/questions/2369492/generate-a-heatmap-in-matplotlib-using-a-scatter-data-set#2371812