if fields.start and fields.finish not set in trac.ini, use datetime of 'accepted' and 'closed'
|Reported by:||falkb||Owned by:||ChrisNelson|
This way, if we don't schedule tickets, we could use this Gantt chart as time survey over the done activities.
This is somehow related to #8786.
Addon: we also have the ticket state 'testing' before 'closed'. Would be cool if the Gantt chart bar changes the color after the state switch.