Add controler for low demand times

[mschnepf]

COBalD needs at least one running resource to determine utilisation and allocation. Therefore at least one resource (supply > 1), e.g. one server, is running only to check for demand. The demand for some resources is infrequent or only at a given timespan/date. If there is no demand for a longer period, resources are only requested to check for demand.
During a no-demand phase, the new controller sets the demand>0 in intervals. If the resources are inefficiently used, the demand is set back to 0 until the next interval is over. This would reduce resources that are requested only to check for the demand.

This could be useful in combination with the Stepwise controller. This new controller is used during a low supply time to check from time to time the demand. Another controller is used during high supply phases.