Validate config with JSON schema

[vjpr]

Would help catch typos in the config.

[asztal]

Looks like Webpack 2 does this itself :)

WebpackOptionsValidationError: Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
 - configuration.module.loaders[2] has an unknown property 'queries'. These properties are valid:
   object { enforce?, exclude?, include?, issuer?, loader?, loaders?, oneOf?, options?, parser?, query?, resource?, rules?, test?, use? }