Decide on handling of bounds sequence

[Vindaar]

Decide on the best way to handle the user given sequence of tuples storing upper and lower bounds for parameters. If the user hands such a sequence (s.len > 0 checked), we need a way for the user to hand only a single bound on one parameter.

Previously one needed to hand (-Inf, Inf) as a tuple for these parameters. Now we interpret all bounds as unbound, if upper value equals lower.

This however disallows fixing a parameter to a certain value.

Find a good solution?!