Add ‘keepstream’ option to Plotly.Plots.graphJson.
Add ‘keepstream’ option to Plotly.Plots.graphJson.

Previously, calling `graphJson` only had the following options:

* `keepdata` (remove src keys)
* `keepref` (remove raw data if src exists)
* `keepall` (don’t remove anything)

This adds a new option:

* `keepstream` (remove raw data if src exists and stream is not in obj)
plotly/plotly.js,etpinard/plotly.js,iongroup/plotly.js,asolagmbh/plotly.js,iongroup/plotly.js,aburato/plotly.js,etpinard/plotly.js,plotly/plotly.js,asolagmbh/plotly.js,iongroup/plotly.js,asolagmbh/plotly.js,plotly/plotly.js,etpinard/plotly.js,plotly/plotly.js,aburato/plotly.js