Make dev environment more closely match prod, and prod match itself

[ian-r-rose]

A few things to audit:

1. The prod python environment(s) have some historical cruft. Maybe we should recreate them de novo (possibly with conda, cf switch to miniconda in dockerfile  #64)
2. There are at least two prod ec2 instances, which may have diverged. We should audit to see if there are significant differences. At the very least, the way the application is deployed is different
3. We should likely lock down the environment a bit more by specifying versions in the requirements.txt.
4. We should swap out the Postgres backing database for a MySQL one in the dev environment to match our prod setup.