New codegen logic in codegen/
New datatype classes generated into plotly/datatypes/ (These are gitignored)
New validator classes generated into plotly/validators/ (These are gitignored)

Code generation in update_graph_objs.py modified to map Figure, Layout, and Trace types to new plotly/datatypes/ classes. All other classes mapped to raw dicts/lists.

It's now possible to execute a fair amount of legacy graph construction and plotting code

TODO: add support for datetime arrays in validation and in widget serialization

Added js/ directory containing front-end widget library
Added graph_objs.FigureWidget class that maps to datatypes.FigureWidget

These are mostly just for discussion during the WIP integration process.

…mpy arrays