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.
> you're actually opening yourself to a potential infinite spawn loop

I would posit that that's not a concern of the build script.  If a project is incorrectly configured, that's not my problem insofar as I should have informed the use how to have a properly configured server.

And, in our case, it calls `node ./bin/www`.  Decoupling the script from those kinds of concerns was my intention.  If, for some reason, we swapped out our server for another one that was started the same way, I wouldn't have to modify the build script.  It would "just work".