Add Google Cast Integration

I'm not referring to the capabilities of casting from Play Music, I'm referring to being able to cast from ANY application that supports casting in general. This would also allow pairing of Google Cast devices with Sonos devices, and open up the ecosystem for Sonos to many more apps and services. In addition, the hardware already exists, as the setup process is identical to non-Sonos devices. This would be a huge boon to me, as I'm an all-out Google person and will be switching to Google Cast devices if support isn't added.