Filtered subscriptions

[MikeBishop]

I notice several of my pistons run when they don't actually need to. This may just be a limitation of SmartThings and event subscriptions, but there are a wide variety of events which can be referenced in a piston which don't need to be subscribed to 24/7. They basically boil down to patterns of A && B && C; if A is currently false, events from B and C are irrelevant and can be ignored. (For example, my logs are filled with motion sensor triggers by my cats while the location is in a mode that doesn't actually do anything when motion is detected.)

(Events of the type "rises above" or "stays" do this too, though that seems somewhat unavoidable. They might be handled in a layer above the piston, but something still has to run enough to see whether the condition has returned to a state where the event can take place in the future.)