Begin migrating test framework to Jest

[hamilton]

This is part of #807. Metrics Graphics is a really large library, and one that is largely tested visually. Total nightmare. Refactoring and pushing toward more testable, cleaner code (#811) requires refactoring to deal with smaller code chunks, removing side effects, and thoroughly writing tests around the smaller quantities.

The first step should be straightforward - let's set up a jest-test script for now (so it doesn't clash with the current test script) and begin migrating out the tests into that, refactoring as we go. We can begin populating a jest-test directory until we feel we have comparably bleak coverage, and then replace qunit altogether.

@wlach if this sounds good to you I can make a PR that accomplishes this.