Store.Import copies every member of every file group and the images
and videos under PRIVATE/M4ROOT to dest/YYYY-MM-DD/<file name>. The day
comes from the new Object.ModTime. A file group stays in the folder of
its primary member.
Each copy is read back and compared by SHA256. A file with the same
hash already there is skipped, and anything else there is a conflict
and left alone. One failed file does not stop the others. A cancelled
context stops at once and removes the partial copy.
Object.Hash now shares its reading code with the import.
Model: opus-5-5