Added command to start datasource

Handy little script to start the datasource with the xcore script itself.  You can currently run it with just `xcore server`.  The logs from the command are written to the console just as if you had run it directly.
All `npm start` does is call `node node-datasource/main.js`. And incidentally, `npm start` by default will actually run `node server.js`, by design of npm so here you're actually opening yourself to a potential infinite spawn loop.

The xTuple Server (1.0 was released last week, btw) uses [forever](https://www.npmjs.org/package/forever) to manage and monitor the server processes and auto-restart on boot, etc.. The xTuple Server is specifically designed to be extended and modified -- it's a development platform in itself -- so if you'd like more info on customizing it to work with this project I'd be happy to help you with that.