Use webpack.NamedModulesPlugin in dev

[sophiebits]

Can we use webpack.NamedModulesPlugin in development mode? Apparently it will make module factory names show up correctly in the devtools (see webpack/webpack#4858).

[gaearon]

Sounds good! I didn't realize. Want to send a PR?

[Timer]

I would love to see this done alongside #2328 (since it introduces this plugin anyway).

[sophiebits]

This can probably be done independently of #2328 too, but I'm happy to have someone new take a stab at this and verify that it works.

[Zaccc123]

I updated it locally and generate a new app to test, the profile in startup does look better:

[sophiebits]

Looks awesome.

[gaearon]

Fixed in #2458.
Sorry for slow review—some React stuff has been taking my time 😛