[ABW]: [Fix] database_api.find_votes now limits response to 1000 votes like in fat node

find_votes SQL routine now comes with limit (but limit is 1000 everywhere which might potentially influence vote listing in various API calls, on the other hand it might be seen as safety measure)
[Fix] valid_number now properly treats 0 according to lbound:ubound instead of always as an error (influences border case of limit param and specific value of score param)
[Change] database_api list_comments/list_votes now have default value (1000) on limit parameter (which became optional)
[Fix] checks on database_api find_comments: comment param must be a list; no longer fails on elements that are not (at least) pairs of strings or on (effectively) empty list