Re-encode books with updated metadata

[knicholson32]

Is your feature request related to a problem? Please describe.
When parameters are altered in unabridged relating to a book (title and description, for example), those values are exclusively stored in the unabridged database: they never make it to the actual file stored on disk. This is an issue because it means that Plex and other apps (like Prologue) don't reflect the updates.

Describe the solution you'd like
When parameters are edited in unabridged, those books should be queued for re-encode automatically.

Describe alternatives you've considered
This may or may not require re-writing the AAXtoMP3 subsystem. At the very least, ffmpeg should be ran to add the pertinent values. However, other libraries may need to be used for alterations relating to the cover image.