Add a toggle for Smart Away

[ianiv]

The Smart Away scene in the Lutron app is great and it would be even better if we could control it via the Home app or automations. It could be exposed as a toggle switch.

I found gurumitts/pylutron-caseta#78 which appears to document the relevant LEAP messages.

I might take a stab at this if I find the time, but if someone else wants to give it a try I'd be forever grateful :)