Dropping Javelin Support

This is labeled as an 'enhancement' even though it obviously is not. That's because these ticket categories aren't really designed for breakage, so perhaps this should be reframed as moving to an outside repo?

Pinchord will be dropping Javelin support in Pre-release 31, as its too much of a burden to maintain.

I think making a Javelin port of Pinchord that doesn't have perfect parity but works well enough would be a good idea, but I don't really care to do that right now. This would be in a separate repo, and not be able to do as much as the Plover plugin, but the same amount really that it can do now.