Webpack task options should be split from webpack config overrides

@christiango 2019-07-10 18:47:30发表于 microsoft/just

The options to the webpack task achieve 2 things:

  1. Configures things for the actual just task (nodeArgs, path to config file)
  2. Passes generic overrides to the webpack config

This resulted in a bug that is addressed in #174, but we need a better long term solution, such as putting the config overrides under a configOverrides property on the task config