Improve readability of webpack config

Created by: uniqueumang

Improved readability of webpack.config by removing redundant code & hence making it simpler to read.

There should be no change in overall output with current master. Following have been locally tested:

1. In production config, code generated is minified (see screenshots).
2. In development environment, code generated is not minifed.
3. SourceMap is enabled in Prod & dev environment by default.
4. By setting GENERATE_SOURCEMAP to false, causes sourcemap not be in generated in prod environment but continues to be generated in dev environment.