Server builder refactor

This isn't finished. Still need to

- [x] Do the same for netty-server. This is just a jetty server builder.
- [x] Decide on the right migration name/package. *Taking over the name 'Server'*
- [x] Should we start moving more towards a convention for `uppercased` file names? *Yes, when the name of the file matches the name of all types within it.*
- [x] Add in support for resources to the jetty server builder.

Anyway, it passes as many tests as master does (`unfiltered.request.GzipSpecJetty` fails?) so that's good.