Run `yarn add/remove` and `npm install/uninstall` on eject

[gaearon]

We currently don't update lockfiles after ejecting. This might or might not work depending on what npm and Yarn choose to do. Let's fix ejecting to update lockfiles.

[Timer]

#3347 if anyone wants to pick it up

[gaearon]

I verified #3806 is enough both for npm and yarn.