Created a pm2 web interface.

Seeing the potential in `pm2 web` I decided to add some more functionality. This pull request adds:

* `pm2 web start|stop|restart`
* A dashboard with some functionality. Displays processes and CPU's etc. See screenshot below.

I'm merging now to test the waters. Should I continue with the web interface? And if so, should I add the ability to start and stop processes? I can see some security issues arising but could be alleviated.

![screen shot 2013-06-28 at 00 36 07](https://f.cloud.github.com/assets/621110/719419/cf9a228c-df82-11e2-84a9-8540ccd66490.png)