Separate out docker support

[fsgeek]

This is a work tracking item since I'm already working on dis-entangling the docker support from the DB config support.

Docker has an SDK for python, so that makes managing the container(s) a bit easier, though I don't have a particularly general model for doing so at this point. Part of the motivation for this was Margo asking about adding full-text indexing. I don't think it is worth spending much time on this (e.g., building it) but it does make sense to spend some time to simplify updating the container without losing the database or wiping the database without changing the machine configuration.