Snakemake pipeline refactor

[wtbarnes]

Fixes #10

This is a massive overhaul of the entire pipeline to use Snakemake as an orchestration tool. This makes it much easier to lay out pipelines that have fairly complex dependencies over many different steps and pieces of data.

Additionally, this also introduces the possible configuration for the second overlappogram

TODOs

• [ ] Adapt SpectrogramChannel class to include the second proposed overlappogram
• [ ] Adjust reference pixels for filtergrams and original overlappogram to accomodate new overlappogram
• [ ] Move PSF step to be "detector level" calculation
• [ ] Parameterize PSF for new overlappogram
• [x] Implement instrument intensity cube calculation step
• [x] Implement overlappogram projection step
• [x] Implement component summation step
• [x] Clean up all the old pipelining code that preceded this refactor

[wtbarnes]

I think it might be better to move the addition of the extra overlappogram to a separate PR.