BoxClustering does not work with LGG09

[schillic]

LGG09 constructs TemplateReachSets with typically some dimensions undefined. BoxClustering expects fully bounded reach sets and is the default method. So using LGG09 in hybrid systems fails by default. We should either change the default or (better) detect unboundedness (we could let the continuous solvers provide this information instead of computing it from the set) and print a helpful error message.