This saves around 3 MB binary size by not including useless fomantic
files in the build. Also, this allows us to move jQuery into the main
bundle as well which eliminates a few HTTP requests.

Also included are webpack config changes:

- split less and css loaders to speed up compliation
- enable css sourcemaps
- switch css minfier plugin to cssnano-webpack-plugin which works better
  for sourcemaps than the previous plugin

Co-authored-by: techknowlogick <techknowlogick@gitea.io>