CSL/CTMC, Simulation: Steady-State operator, functional tests

[ivan.zapreev]

Add functional tests into the test suite for testing the behavior of the steady-state hybrid implementation (simulation engine). First add simple tests - already there, later create new larger test cases.

There is one large test there now. The additional testing will be done using the performance tests. The same will go for the pure steady state simulation algorithms.

[ivan.zapreev]

Due to the poor performance of the regenerative method, we do not have large models in the
functional test suite that terminate within reasonable time.