Store fields in a canonical order.

While it doesn't have any practical effect on the data, storing information in a canonical order helps maintenance of the files.

I'm working on a script that does the sorting automatically, but it takes so long to run on legislators-historical.yaml (because of the YAML parsing and output) that I'd like to get this into master while I continue to work on the script itself.

Note that this work helped to uncover a few issues in the data, and I hope to incorporate it later into some sanity and integrity tests on the data.