This control object allows access to the internal working set tables of SimTree.

These tables contain the work items which SimTree has to handle. The list
of work items is initially build from the current content of the results tree
and from the options [@o]--simulation-parameter, [@o]--simulation-parameter-path and
additional options like [@o]--force-all-values. The working set contains three
tables: The wait-queue which contains work items which wait for a process
slot to be handled; the run-queue which contains work items which are currently
in work and the finished queue which contains all entries which are completed.
