Remove usage of cloned ISimulation for sample model creation

This MR removes the necessity to clone an ISimulation object while running unit tests. With this, further simplifications can be realized (see #98 (closed))

requested review from @j.wuttke

mentioned in issue #98 (closed)

Almost frightening how easily you could achieve a far-reaching simplification.

approved this merge request

mentioned in commit ca6c2ffa

merged