stagger input polling

Previously, every set of inputs would be polled once before any change
in the input state was reported, leading to an average delay of 2
polling cycles before any given input would register.  By reporting
changes after *each* set of inputs is polled and staggering the sets, we
reduce the delay in the case where more than one set is triggered (e.g.
multiple sensors under one panel).

So for four sets of sensors, triggering:
1 sensor = same average delay
2 sensors = 2/3 average delay
3 sensors = 3/8 average delay
4 sensors = 1/4 average delay
make actual inputs a compiler constant