Get main.py driver ready for running sim data EDA

- various arrays of input variables to tweak are now
  in main.py

- filter_phot has mag_max = 28.5. This is hard coded
  in this module so will run the sims separately for
  each different mag_max. The other variables can be
  handled by a loop.

- next commit: make separate modules for:
  a) Likelihood code as a function of input parameters.
  b) diagnostic output plots.