MOB-1806 Pin type parent

Add new parameter for POI categories list (parents=1)
Do we really need it to be an integer? Basically, whenever the parameter is set we want to select only parent categories. Maybe it makes sense to change the parameter name to `onlyParents` and don't care about its value -- just check if it's set if it is then we add `WHERE` to the SQL statement. Am I missing something?