Set up Jenkins build

[caufieldjh]

Sub-issue of #39

This build process already relies on the ODK Docker image, so it's most of the way toward being automated.
Another consideration is that retaining previous build artifacts is preferable so we don't frequently re-download components unnecessarily.
It also needs access to at least 32 GB of memory (edit: in practice there is a memory peak of more like 24 GB) and ideally should push artifacts to GH releases, rather than just storing them on S3.