Refactoring/optimization of IsoformPlot

[jsaquing]

Goals:

• more control over visual format of plotted objects
  • i.e. need to better separate code that handles adding objects (abstract) to plot from code that actually adds Artists (concrete) to Figure
• make it faster to generate multiple plots, potentially involving the same underlying set of transcript isoforms
  • try to reuse Artists and Axes between plots if possible

[jsaquing]

Idea: create JSON-based format for representing all information in a plot (i.e. tracks, genomic coords of each region/marker, formatting, text) and "plotters" for different backends (e.g. Matplotlib, Bokeh) that create plots based on the JSON objects