Log which process is using port when there's a conflict

[KyleAMathews]

This is too cool — added recently to create-react-app facebook/create-react-app#816

[vinnymac]

I would love to see this type of thing used in more modules. Small additional request, improve CLI UX by adding chalk for color in output like they do in create-react-app. If you think the colors should be a separate issue that is fair, we could even add them to the existing codebase without requiring these changes.

[KyleAMathews]

@vinnymac yes! Would love to hear your ideas for improving the CLI UX of Gatsby! Also feel free to port over more ideas from create-react-app :-) They've been doing a killer job and we've already borrowed several ideas and once 1.0 stuff starts solidifying, I'd like to port a lot more but feel free to create issues & PRs in the meantime!