This commit allows NPM to run the client in development and production modes using all the Meteor-related configs.

Run client in development:
NODE_ENV=development npm start
or
npm start

Run client in production:
NODE_ENV=production npm start

The default rootURL is http://127.0.0.1/html5client. This can be changed in .npmrc.
If prodHome is specified in .npmrc, then its value is used as Meteor's $HOME.