Latex node labels in graph visualizations using Bokeh

[bhpayne]

As far as I can tell, Bokeh supports Latex via MathJax (see https://docs.bokeh.org/en/latest/docs/user_guide/styling.html#adding-mathematical-notations ) but not for node labels on graphs. https://docs.bokeh.org/en/latest/docs/reference/models/graphs.html

This is a subset of #19

Using Bokeh for graph visualization would be in the same space as the current approaches, d3js and graphviz. See also #237