IDEA gets super confused when you take a jar task and make it not a jar task.
These are only really used when running from CI (running `./gradlew jar` in
meta will still trigger all of the `:plugin:XXX:jar` tasks), so the names don't
matter.

Try without using gradle's parallel function (probably adds more
overhead for the tiny number of tests we have), and combine
coveralls with the main test run.

Build meta, not just plugins.
Expose plugins as artifacts.

Fixes DMDirc/Infrastructure#62

This saves us using --refresh-dependencies willy-nilly, which
wastes loads of time on the non-dynamic dependencies.