Implement live JS reload functionality

[goshacmd]

This also needs

• a new release of commonjs-require-definition with require.reset support
• a new Brunch release with the bumped commonjs-require-definition

[goshacmd]

A sample React/Redux app that will work with this (and the unreleased commonjs, + custom saving store in global and react-proxy handling) — https://github.com/goshakkk/brunch-livejs-reload-stage1