semi-random tentative crappy code for improving quest aborting, especially when the quest owner has left the party
add extra Debug tools useful for quests
add Cancel option to API for quests that have not been started (invitation stage)
improve new code for cancelling quests in invitation stage and for handling the cases where the quest owner is no longer in the quest or in the party
remove dev comment
Merge pull request #4002 from Alys/questAbortFix

add Cancel button for quests, allow party to cancel/abort if quest owner missing, add Debug tools for quest testing