Save stats "x hours read in total" after finishing e-book#310

After finishing an e-book, my Kobo tells me how many hours it took me to finish the book (with an average read speed, but I don’t care about that). It would be nice to save the reading time when setting a book to finished on Literal, to keep these stats together with the reading dates.

This would also tie in beautifully with monthly/yearly reading stats I think, if they may become a thing in the future.