Feature suggestion: persistent progress save and optional sync by title and author

[ohnoitschair]

I organize my books by folders based on Calibre metadata, and whenever any of that changes, for example, when my progress switches from unread to reading to favorites, books move around and the progress gets lost because it's based on paths. It would be nice to have an alternative where progress is saved based on unique metadata like the book's title and author, so wherever that book is located, the progress is preserved.
Also, even with how the progress is saved right now, if a book is re-uploaded, all cache gets purged and the progress is lost, even if the book is re-uploaded to the same path. I suggest when a cache wipe is triggered by a re-upload, delete everything in the cache dir except progress.bin. I'm pretty sure that's where the current chapter and page point is saved to.