Etienne 3d objs

- meta for 'scatter3d', 'surface', 'scene', 'zaxis', and 'error-z', 
`PARENT_TREE.json` isn't used currently. 

The `config.json` files contain its information (set [here](https://github.com/plotly/graph_reference/blob/master/scripts/run.py#L255)  and templated [here](https://github.com/plotly/graph_reference/blob/master/scripts/run.py#L25) and displayed e.g. [here](http://i.imgur.com/xirm3eo.png))

I thought that maybe down the road we could use `PARENT_TREE` in the API `help()` functions, explaining why it is an output of `run.py`.