Cancel-option in __init__() of Simdex when existing

[rubenbaetens]

The init()-function of the Simdex raises a (y/n)-question to overwrite the h5-file if this file yet exists. When entered "no", an Error is raised and the script is aborted.

It migth be favorable that, when entered "no", a second question is raised "whether the existing h5-file is the h5-file you were intending to make and work with, yes or no ?" whereafter the script continues with teh existing h5-fiel without overwriting it.