Add notion of time randomizer

[dhylands]

Not sure if this is the right place to put this but when scheduling things like lights, it would be nice to say things like:

Turn my outside lights on at sunset plus or minus a 30 minute random time interval.

[Yoric]

I was thinking about adding a delay to the condition, but we can also add one to the execution. So instead of When [x] do [y], we can also say When [x], wait [min, max] seconds then do [y], or if we use both delays, When [x] has remained true for [t] seconds, wait [min, max] seconds then do [y].