Relative file and folder paths - a simple solution

Is your feature request related to a problem? Please describe.

The problem is that if I want to store my photos on a network drive or an external disk and connect to the photos from different machines with different operating systems darktable wont be able to find the photos since the paths in the library.db are absolute file paths.

Describe the solution you'd like

The solution I would like is similar to the catalog system in Lightroom where if someone chooses to store the photos in a folder that is in the same place as the catalog (library.db in darkroom's case) the photos will always be adressed relative to where the catalog is.
In the case of darkroom I would store the library.db also on the external or network drive and darkroom would store the locations of the photos and folders relative to the location where library.db is.
Like this there would no GUI changes. Darkroom would simply import photos relative to library.db if the photos are in the same folder als library.db. A quick note in the manual suffices (for now).

Alternatives

Additional context

Start by tracing how darktable stores and resolves photo and folder paths in library.db. Define how locations should become relative when photos are on the same drive or folder as the catalog, including behavior across operating systems; done means those photos are found after moving the catalog and media together.