Make the time series photometry figure for the paper and add text describing it

[gully]

We have copious photometry data! Let's make a figure with these elements:

1. K2 data from 3 campaigns, vertically registered to K2 zero-points.
2. ASASSN data
3. Vertical bar of IGRINS epoch
4. Celerite model fit threading through both the K2 and ASASSN data.

We've already done this for posters, so we should translate that work into a paper-sized version. We also need to describe in the text what we have done to create this figure and what we learn from it. In particular:

Can we assign the starspot coverage fraction at the global peak-and-valley?

[gully]

We should update the ASASSN photometry to 2020.