Link given app source and dependencies from local file system.

@param {String} app Path to the module to link.
@param {Function} callback Callback to run once work is done.
function (app, callback) {
    var options = {
      local: true,
      dir: configHelpers.getModulesPath(),
      prefix: ''
    };
    npm.load(options, function () {
      app = pathExtra.resolve(npmHelpers.initialWd, app);
      npm.commands.link([app], callback);
    });
  }