Version 4 make_subplots enhancements

[jonmmease]

Meta-issue summarizing the plotly.tools.make_sublots shortcomings we would like to address for version 4.

There are a bunch of outstanding issues with the make_subplots function. The most significant limitation being that it doesn't support non-Cartesian subplot types.

When we integrate plotly_express into plotly.py for version 4, we need to make sure the subplot approach used by plotly express and the subplot approach used by make_subplots is compatible. i.e. it should be possible use add_traces(..., row=2, col=3) to add new traces to plotly_express generated subplots. I think the most direct way to accomplish this will be to grow tools.make_subplots to be able to support everything that plotly_express needs.

I would also like to add support for accessing traces by subplot. Something like
figure.get_traces(row=2, col=1). This would allow users to construct an initial figure using px, and then easily grab particular traces to customize using .update or property assignment syntax. See #1484 for some more discussion on accessing and updating subplots.

Finally, it would be great if make_subplots could also provide some support for the matches argument added by plotly.js (https://github.com/plotly/plotly.js/search?q=matches&type=Issues).

[jonmmease]

make_subplots rework done in #1528, select_traces will be done in #1534