Custom Middlewares

Added the option to add custom middlewares, you can enablebyFolder and then you can export a array containing the middlewares in store/middleware like:

export const middlewares = () => []

export default middlewares

It is also possible to add them to the config in middlewares.collection, with this option it is also possible to add different middlewares for different environments.

Satisfies #13

Also solves warnings in the console for the webpack-image compiler