Jasmine stack trace output (shown when a test fails) is hard to debug
with Babel. Fortunately, there's a useful third-party module called
sourcemapped-stacktrace.js, which can take a stacktrace and apply
sourcemaps. This change introduces that module and a new custom module
for Jasmine that will use this for all resulting stack traces.

Ran some failing unit tests where ES6 code was involved. Saw that instead

of seeing generated JavaScript output referenced in the stack traces,

the original source filenames and lines were shown instead.