Add alluvial plots to summary stats script

[rjcorb]

Purpose/implementation Section

What scientific question is your analysis addressing?

Closes #20. This PR updates 02-summary_stats.R script to add alluvial plot showing concordance between predicted ancestry, reported race, and reported ethnicity in PBTA ancestry cohort.

What was your approach?

• formatted metadata df for alluvial plotting
• generated plot without legends
• created three separate "legend-only" plots for predicted_ancestry, race, and ethnicity, and used cowplot() to arrange these with the alluvial plot

What GitHub issue does your pull request address?

#20

Directions for reviewers. Tell potential reviewers what kind of feedback you are

soliciting.

Which areas should receive a particularly close look?

Please review new code for formatting data and generating alluvial plot.

Is there anything that you want to discuss further?

The current code for creating group-specific legends is a bit cumbersome, so any recommendations on how to streamline this are welcome!

Is the analysis in a mature enough form that the resulting figure(s) and/or table(s) are

ready for review?

Yes

Results

What types of results are included (e.g., table, figure)?

What is your summary of the results?

Reproducibility Checklist

• The dependencies required to run the code in this pull request have been added to the
  project Dockerfile.

Documentation Checklist

• This analysis module has a README and it is up to date.
• The analytical code is documented and contains comments.

[jharenza]

Nice plot! I might also suggest writing out the predicted ancestries maybe with abbreviations in parentheses in the legend since every other legend group has them written out

[zzgeng]

Ohh I leave the comment in wrong PR . Approving