* support mathjax header in plotly backend
* support extra_plot_kwargs in plotly backend
* correct local file parameter to `file:///`
* corrections proposed by @BeastyBlacksmith
* include extra_kwargs for subplots
* don't merge subplot extra_kwargs
Co-authored-by: Helmut Haensel <M136270@eu.merckgroup.com>
Co-authored-by: Simon Christ <SimonChrist@gmx.de>