Motivation:
* too many conditionals for config, better to be explicit
* different priorities: faster build for hot mode
* working SCSS sources for styles in hot mode
The biggest differences:
* removed linter from TS loader in hot (should be editor or precommit
or responsibility)
* simplified styles loading
* hot needs more extensions to resolve
* removed commons chunking for hot
* removed devServer from dev
Reduced HMR time from 8s to 4s on my machine.
