V4 -- Add dependency to cssmodules on installation

In order to support setups with and without cssmodules, starting with [v2.0.1-4](https://github.com/react-webpack-generators/react-webpack-template/releases/tag/v2.0.1-4) of the template we removed all hard dependencies to it, including listing the module in `package.json`. In order to support setups with `cssmodules: Yes` we need to add this dependency programmatically.
