Fix autocompletion for site usage & compartment

While reviewing !401 (merged) we realized that there is some problem with one of the features of the select boxes (typing in the field and getting a subset of the original list) doesn't work for site usages & compartments.

Both have in common that there is a next select list that is filtered by the selected site usage (-> site type) or compartment (-> sampling medium), so trigger/watcher logic may be involved here.

Nevertheless it is the task here to fix that, so that I can start typing Art and I have only Artifical area in the select list left (or similar - I don't remember exactly how the real world values are).