Nuke the shrinkwrap (& other things) 

- Removes the npm-shrinkwrap, as it breaks most fresh installations
- Lets us look in node_modules for generators (designated by
  generator.json files present in a module)
- Uses brunch-jsenv to allow us to have config variables that depend on
  the environment before they are compiled. This will help remove
  context-specific variables (like API urls) from the actual codebase

@jhabdas ?