More notes on dye release models
Addition of lipo_sites binding model and new models in core

New models in core for fitting dye release titration data with Bax at
43C.
Moved generic elements of NBD_MCMC to a new class

The new class, tbidbaxlipo.mcmc.MCMC, contains the enhancements to the
underlying bayessb.MCMC that are useful for working with builder-based
models with complex observables, but aren't specific to NBD fluorescence
modeling.

The idea was to extract these features so as to build a new class for
fitting dye release data.
Deprecated nbd_mcmc_pt and _run in favor of MPI versions

Simply moved them to old/, so I can still use them if need be.
Initial commit of a class for fitting dye release models
Added function to plate_assay to use pandas DataFrame

Also included the boiler plate code to put together a dataframe with
hierarchical rows and columns in util/pandas_test.py
Eliminated unnecessary imports in nbd_mcmc
Initial commit of init-able PoreMCMC class
Implementation of PoreMCMC.plot_data
PoreMCMC.fit_plotting_function works now
PoreMCMC fits can be run and reported on

I had a bunch of detailed notes in a commit message but I didn't commit
it right and then I deleted it. Oh well. You'll have to look at the
changes and figure it out.