Potentially removing brunch from the Phoenix new template generator

[chrismccord]

@peerreynders

I would also imagine that npm scripts would be a very effective way of communicating most of the information needed when somebody wants to use their favorite build tool instead

This is already easily achievable today by swapping out a single line in your dev.ex :watcher configuration. For example, swapping brunch for webpack is maybe a 30s affair today.