Make graph_objs.py compatible with new graph reference!

- created from @theengineear 's factories branch
- adapt graph reference INFO to new graph reference structure
- add doc content (e.g. links to plot.ly examples and parent keys for a given obj)

Yeah, I agree. I made consistent with graph [ref](https://github.com/plotly/graph_reference#the-graph-reference-structure) though.

We'll converge to something at some point and it won't be too hard to change.