make spacebrew "require"-able

This pull request allows spacebrew to work as a dependency in other node.js projects. You can try this locally by typing [npm link](http://justjs.com/posts/npm-link-developing-your-own-npm-modules-without-tears) in the spacebrew directory. It would be great to have this published on NPM also.

I used this with Node + Express for bundling spacebrew's server, admin and sketches under one process.

- server logic now in index.js so spacebrew can be used as a library through spacebrew.createServer
- added package.json so spacebrew can be installed as a dependency
- "npm start" command aliases to "node node_server.js"