Tidy up some build logs

Created by: gaearon

• Hides [CaseSensitivePathsPlugin] prefix for errors from case-sensitive-paths-webpack-plugin since the messages are descriptive enough.
• Hides the Total precache size is [...] message from sw-precache which is noisy on every build. I let the other messages pass through as ejected users might misconfigure it and will likely want to see them in this case.