Move CI to Tiger

We have been using Travis for CI, but they are now setting limits that we have exceeded.

Rubin moved their Travis operations to GitHub Actions, but they only use it for linting, which is fast. We've been using Travis for integration testing, which takes much more compute power (we only have a handful of packages, so we could get away with it), so we're in a different regime.

I propose to move our CI to Jenkins running on Tiger. We already run weekly production runs and builds through this mechanism, and it wouldn't take much to extend it to run smaller-scale integration tests on demand.

• Write a back-end script to run the integration test under Jenkins, and report the results via e-mail and/or Slack.
• Add Jenkins job.
• Add a front-end script to trigger the Jenkins job.
• Remove Travis.
• Circulate instructions.