Gracefully handle initial npm errors

[gaearon]

Currently, when npm fails for the first time, you end up with an empty project that doesn't work.

We should delete the broken files we added (or the whole folder if we created it), and print a message explaining the problem is with npm, as well as the underlying message.

[chitchu]

Hi @gaearon

I would like to work on this. Any tips on which files I should be looking at?

[Timer]

@chitchu https://github.com/facebookincubator/create-react-app/blob/master/packages/create-react-app/index.js#L173-L195 should be a good place to start.