Generate forecasting information that combines CHIME and IHME

[lossyrob]

The goal of this issue is to create an easy-to-consume way to generate forecasting data from IHME and CHIME data.

Currently IHME is only by-state, so this combination will be at the state-level until #79 or IHME releases county level data.

The dataset should have a normalized format - for instance, CHIME produces day counts while IHME has dates.

Documentation should be made to describe the most comparable columns between the two datasets.

[daveluo]

Re: integrating CHIME model and running it on regional levels, @lossyrob is making headway on this at

• Create dataset of CHIME model predictions per US county #79
• https://github.com/covidcaremap/covid19-healthsystemcapacity/blob/master/notebooks/00_getting_started/02_Working_with_demand_data.ipynb
• Add RegionalSirModel. CodeForPhilly/chime#272

@jsfenfen is interested in running the CHIME model at CBSA and State levels too so looping in here.