Add support for non-standard "srcDir"s in module.js

[JorgenVatle]

Added support for users who wish to keep their generated files in a custom non-root directory.

[JorgenVatle]

Added support for usage of shared Nuxt environment variables for specifying Socket.io URLs. 👍

// ~/nuxt.config.js

module.exports = {
...
  env: {
    nuxtFeathersUrl: process.env.SOCKET_IO_URL || 'http://custom-url-here:1337'
  }
...
}