[Feature] Complete date/time metadata overhaul

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request. • Yes The feature The immediate issue I filed in the metadata thread is that the default timezone field in the YML file seems to have been broken by server v2.4.1. That can be found here: I figured I may as well take the opportunity to outline a complete, future-proof overhaul of the date/time metadata system in external libraries. Feel free to implement this in stages. I'm sure some of this code might work well for other setups too, but it would make a night-and-day difference in external libraries. Existing Workflow Explicit Metadata ↓ GPS Location ↓ GPS/manufacturer UTC timestamp (lost during photorec and some cloud downloading services) And it gives us annoying problems we all put up with, such as: • Android videos universally shown in UTC • FileModifyDate photos (i.e. no metadata) shown hours ahead or behind their ac…