Allow variable {author} in the "Move to" field in the rename dialog box

[ecrin4102]

For people like me who want to place books inside the author directory, it should be very usefull to allow {author} in the "move to" field during renaming process. I can develop myself if this request is accepted.

[sonaton]

use template {path(author)}{title} - {author} or {author}\{title} - {author}