Adds Bayesian plots to Python (#52)

* added corner and hist plotting (without smoothing)

* added normalisation to plots

* added bayes shading to ref-sld plots

* added plot_bayes

* small refactor to plot_hists

* refactored to use panel plot helper and added plot_chain

* better error handling and can now use subset of indices

* added contour plots

* rearranged and added estimated density plotting

* added new deps to setup py

* debumped scipy version

* added smoothing to hists

* review fixes and rewrote corner plot from scratch

* fixed corner plots for subsets

* simplified assert bayesian

* added error for shading plot and wrap for corner titles

* added unit tests and associated fixes

* fixed bad loop

* added smoothing parameter, fixed panel layout, removed use of x data

* readds x-data for now

* review fixes and added shading test

* fixed plot hists

* made hist panel test better

* review fixes and better test coverage

* simplified estimated density standardisation

Author: alexhroom