changed field label in subject visit info https://git-r3lab.uni.lu/NCER-PD/scheduling-system/-/issues/331\#note_46155

fixed issue with visit numbers in statistics https://git-r3lab.uni.lu/NCER-PD/scheduling-system/-/issues/333\#note_46157

more admin menus. I don't know other way to edit the columns that are visible except manually from psql

small description so that it is not counter intuitive to find first 1 and then 0 in the subject visits

undo change. see https://git-r3lab.uni.lu/NCER-PD/scheduling-system/-/merge_requests/250\#note_46014

in case of SHOW_VISITS_FROM_ZERO, we add another field to the serialization (we don't want to replace visit_number in case is used as such)