The test setup directory is no longer being used

@babel/polyfill is no longer needed as tests in browser are no longer applicable

Since browser tests are no longer applicable, jest is the only tool that is actively using babel.
The target can now be set to the current node environment, which in turn does not require additional
polyfills (core-js, regenerator-runtime, etc)

Update recently added watcher immediate tests to use jest assertions and mock functions over mocha
chai

These dependencies are no longer used and can be removed from the package.json

Since the circle container is only 4GB, running jest tests in parallel is problematic as the
container frequently runs out of memory. The memoryt can either be increased, or the tests can run
in a single thread

Babel is now only currently used by jest or systems under test. These should now be considered
development dependencies

After converting to Jest, browser tests were removed due to capatability issues. This reimplements
the browser tests with similar techniques.

All related webpack/loaders have been updated to use the latest stable
releases

Chrome/HeadlessChrome is now being used to run these tests over the deprecated
PhantomJS

Karma and Jasmine are being used as a test runner while leveraging Jest's expect/assertion and mock/stubbing libraries

Highly inspired by https://github.com/tom-sherman/blog/blob/master/posts/02-running-jest-tests-in-a-browser.md.

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Add back build scripts that were initially removed from jest migration

JSDOM and JSDOM-Global are no longer used with the removal of the mocha tests. JSDOM is still used
implicitly by jest.

Set singleRun option in karma to true locally and in CI so the test process always terminates when
finished