Draft PR: Scoring plots

[SamuelBrand1]

This draft PR tracks the contribution of these scoring plots/tables:

• Table of model performance over season. Required columns: Model, abs WIS, rel. WIS, MAE, 50% coverage and 95% coverage.
• line plot of relative WIS by each week: two curves, 1 is flat (cdc flat baseline) the other is pyrenew-hew
• Heatmap plot of relative WIS by each state over season.
• plot_wis showing relative contribution of under/overprediction and dispersion for cdc flat baseline and pyrenew-hew.

[SamuelBrand1]

I've added a function to summarise the scores by model (over all days) which gives the columns as described at the top.

[SamuelBrand1]

I've added a plotting function for (epi)weekly WIS scores. This might need a bit of tuning for visual niceness.