Add option to use Babel

[danielbayley]

http://coffeescript.org/#coffeescript-2

[n-riesco]

@danielbayley @hoishing we have two PRs open to update jp-CoffeeScript to CoffeeScript 2. The main difference is whether we want to use Babel to transpile or not.

Personally, I favour the option of making transpilation optional (as not everyone needs it and it introduces the import issue).

We could have jp-CoffeeScript do a search for .babelrc (jp-babel does that; see here) and enable transpilation only in that case.

What are your thoughts?

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@danielbayley I'm sorry I have taken so long to act on this issue.

[hoishing]

Maybe we can just update it without Babel first, such that all users can use CoffeeScript 2 right away. Then update with Babel transpilation later if the import issue is resolved.

[n-riesco]

@hoishing OK, I'll merge your PR first.