Flag to retroactively go back and rename old receipts to match the latest naming scheme

[T-Fowl]

Since first developed item ids have changed numerous times, including ddMMyyyy, yyyyMMddHHmmss....$STORE, and now base-64 encoded OpenSSL encrypted values which don't lend themselves to being on a filesystem path.

In ba68fc3 the output path was changed to the generated human-readable filename provided when downloading receipts, and I think it would be beneficial to retroactively apply this (and future) output paths to old downloads.

Thankfully this is possible due to saving the raw json response as sidecar files.