Get Jenkins to set project status, do builds for pull requests, remove Travis

[luser]

I stood up a Jenkins instance that's doing builds + tests for master. It needs a little more fiddling to be comparable to what Travis gives us:

• Set project status
• Build pull requests

Once we get those working we can remove Travis.

[GitMensch]

Travis is not used anymore 85a7671 (since 2022), is this issue going anywhere or should it be closed as unplanned?

[rocallahan]

Yep