Dev version of the dll command

Hello again,

As mentionned in [my previous issue](https://github.com/electron-userland/electron-webpack/issues/105#issuecomment-370155617), I can't manage to have a development environment for the `dll` command (even with `NODE_ENV=development webpack-electron dll`)

I'm using React and need the development version for some reasons (typechecking with PropTypes, unminified exceptions, ...)
I might not run the dll command, so everything is bundled with the `webpack-electron dev` command, but the compiled `renderer.js` is so heavy (~9Mo) that it takes about 5sec between I modify a file and the app is hot reloaded.
In comparison, with the dll bundle generated, the `renderer.js` is about 2Mo and the hot reloading is pretty fast.

Do you know if there's any way to run this dll bundle generation with a development environment ?

Thanks by advance ;-)

Start by locating the implementation and configuration for the `dll` command, then compare how it handles `NODE_ENV` with `webpack-electron dev`. Confirm the behavior using a React application: a development DLL should be usable while keeping the renderer bundle smaller and hot reloading responsive.

Written by the indexing model from the issue text.