Duplicates filtering: Maintain earliest modified time

[pozieuto]

Hydrus now treats the earliest "modified time" as canonical information to be maintained when gathering information from files and domains, but (correct me if I'm wrong) it still seems that it freely discards this when processing duplicates. I would expect it to maintain the earliest time on the better file when marking one as better, and maintain the earliest time on all files when marking them as the same quality.

Another dropdown should probably be added to the "edit duplicate merge options" dialogue for this as well:

• sync modified time?:
  • make no change
  • if worse is earlier, copy from worse to better
  • always copy from worse to better
  • use earliest for both

I think this should be locked on "make no change" when the action is "alternates", like how "sync known urls?" is locked to "sync nothing" in the same situation. The option "always copy from worse to better" was included for completeness, but the usefulness of it is unclear, so it may not be worth implementing.

Not sure if this is really a feature request or a bug, I'd consider it technically "absent obvious functionality".