refactor/clean IHME code

[vishwa-wai]

• moves driver scripts to scripts/ihme
• removes duplicated model running code
• uses YAML config files instead of params.json (which wasn't checked in before either)
  • may need to add yaml to gitignore but we want to keep a few base versions checked in?
• fixes breaks/missing imports etc that happened during previous overall repo refactors
• found a bug in the model that affected optimisation, fixed that
• main/ihme/fitting.py starting to look more like main/seir/fitting.py, but perhaps the output dict should look more similar (will also help viz become model agnostic)
  • some plotting functions still live in main/ihme/backtesting and main/ihme/plotting, need to be moved to viz. ideally, viz functions should be generalised
• adds a basic script to run IHME on all compartments (vs just deaths)
  • modifies models.ihme.population.get_mortality to be get_rates and compute rate/log(rate) for all compartments
  • adds which_compartments function to Columns enum

[vishwa-wai]

some basic docs related improvements are in the works already 😄 and yes - agree on moving configs, but I think figuring out a better way to pass it in will help. reason i put it inside scripts was mostly for ease of passing path in as a command line arg

+1 ideal situation is making models as interchangeable as possible, still a bit more to do to get to that point. I think it will require some mods to SEIR functions as well and didn't want to get into that right now, so left it this way

[vishwa-wai]

and yes - ihme/model contains things that might be better suited for utils/ihme/ - can make that switch