Adding downscaling analysis

[marlinfiggins]

This PR implements the downscaling analysis we discussed previously.

To Do

• [x] Generating data sets at various sequence count thresholds
• [x] Script for running models on these data sets
• [x] Script for generating errors from the truth for these models
• [x] Making sure model outputs are indexed by maximum sequences
• [x] Creating figure showing error dependence on total sequences
• [ ] Computing desired number of sequences for 5% nowcast/forecast error
• [x] Documenting this analysis and adding to READMEs
• [x] Adding downscaling analysis to manuscript