Upgrade frontend build dependencies

This updates several of our frontend build tool dependencies to keep up with bug fixes and performance improvements.

• webpack 3.5.5 -> 3.11.0
• webpack-dev-server 2.6.1 -> 2.11.1
• several webpack loaders
• several webpack plugins
• some karma dependencies

This also closes gitlab-org/gitlab-ce#41400 as webpack 3.11.0 contains the fix we submitted upstream.

https://github.com/webpack/webpack/pull/6176