!!Corner cases and how they are handled

There are some corner cases in handling the simulate and collect runs:

* (IR) Assume that for a simulation parameter value set a simulate run for a
  number i of drops is requested. Then the following may happen

** There are exactly i drop results present. Then the simulate run ist skipped.

** There are less that i drop results present. Then the simulate run
   will add the missing drops.

** There are more than i drop results in the results tree. Then the simulate
   run is skipped.

. This behavior allows differing number of
  drop results for different simulation parameters values sets.

* (BM) Assume that for a simulation parameter value set a simulate run for a
  number i of batches (default batches or seeded batches) is requested.
  Then the following may happen

** There are exactly i batch results present. Then the simulate run ist skipped.

** There are more or less than i batch results present. Then the simulate run
   will remove the existing results and start the simulate run.

. This behavior ensures consistency of the results.
