Added choice of model_demo inside the run_simul function using the set of decisions rules based on :
* lambda (growth vs decline) for DD
* lambda and N0 (small vs large pop) for StochDemo

Updated other functions accrodingly

Added piece "%>% sapply(min, 0.999)" in M3 and M4 to avoid survival parameter > 1.
Also added this in 'init_calib' function.

All models tested and work.