Downloader - Auto-create CBZ after download instead of leaving plain files

[RobbWatershed]

User story : see #847

NB : Several viewer features will be unavailable due to the book becoming an archive

[asl97]

I am interested in this because copying tons of files for backup is very slow.

Even the ancient 'DiskUsage' app, noticeablely takes a while to go through the hentoid folder, currently with ~50k files, number gotten from find /path | wc -l.

Side note: tachiyomi added said feature in Jan 2022 and defaulted in April 2022, citing better performance(?)

Noted that tachiyomi don't normally deal with the 1000s images, potentially 2gb+, archives, that seem common on a certain supported site.