Add mode for defaulting unknown dates to the current month/year

[linucksrox]

My use case is generally that this script runs nightly and moves stuff out of my Nextcloud instance into my NAS. In general, when videos or pictures don't have the right metadata, they are still things that were uploaded either that day or very recently. There should be a mode for this use case to just put unknown stuff into the current month/year.

The unknown date functionality is useful when going through archived stuff, but once you have things cleaned up it's less useful.