Share output from npm during install

[jakirkham]

Would be nice in generated projects to see the output from npm during the pip install both to see what it is doing and aid in diagnosing any build or installation issues.

xref: jupyter-widgets-contrib/ipytree#3

cc @martinRenou

[vidartf]

If you add the -v option to the pip command this should show up. I'm not sure there are any better ways ? Are there any logging calls that will surface this to the non-verbose pip output?