Move away from test_bundle

test_bundle was the best way to go about importing all our specs to instrument and evaluate them even if they have no *_spec.js.

Unfortunately it means we get almost useless stack traces unless you already have some understanding of what should be in the stack at any one time.

Example current stack trace:

ERROR: 'Unhandled promise rejection', TypeError{stack: 'keys@[native code]
transformData@http://localhost:9876/base/spec/javascripts/test_bundle.js?ed63528657d77e7b43eeffb5f30817ada43b2ac5:133549:18
http://localhost:9876/base/spec/javascripts/test_bundle.js?ed63528657d77e7b43eeffb5f30817ada43b2ac5:133349:31
run@http://localhost:9876/base/spec/javascripts/test_bundle.js?ed63528657d77e7b43eeffb5f30817ada43b2ac5:14672:29
http://localhost:9876/base/spec/javascripts/test_bundle.js?ed63528657d77e7b43eeffb5f30817ada43b2ac5:14685:31
flush@http://localhost:9876/base/spec/javascripts/test_bundle.js?ed63528657d77e7b43eeffb5f30817ada43b2ac5:13756:11', line: 133549, sourceURL: 'http://localhost:9876/base/spec/javascripts/test_bundle.js?ed63528657d77e7b43eeffb5f30817ada43b2ac5'}

We managed to do this for the droplab repo and still instrument files that are not yet imported by a spec, but understand our webpack config is more complex.