Internal Sphero IP address is hard-coded into dashboard

[bandrews]

In public/dashboard/src/App.js, an internal IP address (10.211.2.18) is hard coded into the example for determining which WebSocket to connect to. This address should instead be dynamic based on where the dashboard is loaded - ideally, using window.location.origin to auto detect the correct value if the dashboard is hosted on the same device connected to the RVR.