Improve export filename handling
Improve export filename handling

* Note whether all versions or the latest version were included;
* Truncate very long form titles;
* Add seconds to the timestamp;
* Fix #1611 ("values" shown incorrectly instead of "labels").

onaio/kpi,onaio/kpi,kobotoolbox/kpi,kobotoolbox/kpi,onaio/kpi,kobotoolbox/kpi,kobotoolbox/kpi,kobotoolbox/kpi,onaio/kpi