Add custom warning if the value chosen for outer_k in combination with the number of conditions yields too few (inner or outer) test conditions

[PhilippKaniuth]

Some combinations of outer_k and n_conditions can lead to too few test conditions. Catch those, change "outer_k" as it was supplied by the user accordingly, and inform the user. Also inform the user that, when n_conditions is big, the changing of "outer_k" might lead to a much longe run time and that s/he might want to abort and supply a better value for "outer_k".