Added CEGIS control benchmark based on safety_stability.c

Safety_stability.c is the CEGIS input file for the completeness threshold back-end of our state space control synthesiser. Added a benchmark to test CEGIS front-end for this back-end.
# Please enter the commit message for your changes. Lines starting
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# Committer: Pascal Kesseli <pkesseli@dkr13.cs.ox.ac.uk>
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# On branch master
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# Changes to be committed:
#	new file:   cegis_control_benchmark_03/benchmark.h
#	new file:   cegis_control_benchmark_03/control_types.h
#	new file:   cegis_control_benchmark_03/operators.h
#	new file:   cegis_control_benchmark_03/safety_stability.c
#	new file:   cegis_control_benchmark_03/test.desc
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