[mangadex] fix/improve image extraction and downloads (#4247)
[mangadex] fix/improve image extraction and downloads (#4247)

* [mangadex] prepare for new api change
* [mangadex] add throttle for image downloads
* [mangadex] improve image verification (when content-length is missing)
* [mangadex] updated network seeds
ronny1982/hakuneko,ronny1982/hakuneko,ronny1982/hakuneko