DeterministicPrescalers should use a property for a seed

The behaviour of DeterministicPrescaler depends on its name as it uses it for a random seed. In the current data flow framework names are determined automatically, so different prescalers with the same accept fraction end up as one algorithm. The first part of the solution is simple -- just add a property that is used for the seed instead of the name. Then we just have to figure out how to give a reasonable seed.