fix(infrastructure): remove babel loader

[moog16]

related #4225

[kfranqueiro]

This seems to fail npm run build:min whereas the existing config passes. Can we figure out why?

[moog16]

we should have travis run this step. It looks like npm run dist covers both build/build:min. But on 2nd thought it would be nicer to see both build and build:min separately. I can open a PR to update.

[kfranqueiro]

Unit tests are also failing in IE11 due to a syntax error. I don't think we can completely remove babel-loader while we still have ES6-formatted unit tests...

It also occurs to me that even for purposes of just the typescript sources, we probably can't actually remove babel-loader until we remove all occurrences of Object.assign, which probably means we need to wait until after all of the modules are converted to typescript.

[moog16]

I added back the babel loader for js files. I believe it to be unnecessary to have it in both places (ts files and js files`

[moog16]

closing this PR...more to come in #4409