Set up CI/CD pipeline

Looks like I've got a lot of code quality fixes to sort out before we can proceed. This will probably affect a lot of other pending patches and MRs unfortunately; might be a big job.

I think I've worked through most of the code quality issues. I can take a look at some of the other patches that I've been using to work out what to change. There aren't any changes to templates, so most people who've been theming Funnelback pages, blocks and results shouldn't be affected.