upgrade webpack and associated packages

[fryjordan]

Overview

• upgrade Webpack (v4 -> v5)

• " css-loader (v3 -> v6)

• " expose-loader (v0.7.5 -> v3)

• " less-loader (v5 -> v10)

• " style-loader (v0.23.1 -> v3)

• " eslint-webpack-plugin (v2 -> v3)

• " html-webpack-plugin (v3 -> v5)

• " mini-css-extract-plugin (v0.7 -> v2)

• " webpack-cli (v3 -> v4)

• " webpack-dev-server (v3 -> v4)

• remove exports-loader (unused)

• remove imports-loader (unused)

• remove file-loader (no longer required)

• remove url-loader (no longer required)

  Testing recommendations

• automated tests pass

• UI consistent

• run webpack-related scripts (e.g. webpack:dev, webpack:release)

GitHub issue number

N/A

Related Pull Requests

Checklist

• [x] Code is written and works correctly;
• [ ] Changes are covered by tests;
• [ ] Documentation reflects the changes;
• [ ] Update rebar.config.script with the correct tag once a new Fauxton release is made