[Feature request] Allow archive task to not create a new file if it already exists on target

[methedeveloper]

Thanks for this great app! I am using it to backup my photos & videos from mobile to a shared folder on NAS. I would also like to remove old photos & videos from mobile device but archive task creates a new file on NAS if it already exists on target. It would be great if archive task could check if file already exists on target before copying it, or at least allow configuring this behaviour to be optional. I have seen that there is already a pull request #195 that pursues the same idea. +1 for merging this pull request into a new version.