WIP
Sync up and fix style
Use existing Plotly chart type: histogram2dcontour
Implement conversion for geom_density2d
Process the raw data, not the processed data
Fix merge conflicts (sync up with latest conversions)
Fix return of toBasic() for geom_density2d
Merge pull request #88 from ropensci/marianne-geom-density2d

Implement conversion for geom_density2d
getting closer
Merge branch 'master' of https://github.com/ropensci/plotly into xsm-fix-bar-dodge