New system for setting parameters to estimate

Along with a number of other changes:
- Builder now includes an array, estimate_params, in which the
  parameters to estimate are set.
- In addition, there are arrays for parameter means and variances
  for each of the parameters to estimate. These are used to calculate
  the prior.
- The plotting routines in nbd_mcmc_c3 have been broken out into their
  own function, generate_figures, and all figures are included in the
  report, along with the Python code.
Set up core.py and nbd_mcmc_c3 for fitting of c62

Also normalize the output by the initial condition for Bax so that
the scaling factors can be applied to fractions of Bax, rather than
being explicitly scaled according to the Bax concentration.