added exercise12 solution

exercises/ex01_solution/scattering.ipynb

exercises/ex12_skeleton/sim_thermal_annealer

exercises/ex12_solution/Makefile

exercises/ex12_solution/instance.txt

exercises/ex12_solution/plot_succ_rates.py

exercises/ex12_solution/sim_quantum.cpp

exercises/ex12_solution/sim_quantum_annealer.hpp

exercises/ex12_solution/sim_thermal.cpp

exercises/ex12_solution/sim_thermal_annealer.hpp

exercises/ex12_solution/succ_rates-quantum.txt