Webpack config cleanup, fix dev server
Webpack config cleanup, fix dev server

This change tweaks the expression of paths in the Webpack config to make
`webpack-dev-server` work again. This opened the door for some minor
cleanup of `path` & `filename` in the `output` configuration entries.
Thanks to @rschamp for help resolving the `webpack-dev-server` problems.

LLK/scratch-render,LLK/scratch-render