[FEATURE_REQUEST] Integrate isfdb.org as a cover source

[l3if3rik]

Is your feature request related to a problem? Please describe.
Finding covers is sometimes difficult.

Describe the solution you'd like
Integrate https://www.isfdb.org/ as a cover source.

Describe alternatives you've considered
Searching and downloading covers from isfdb.org manually. Frustrating, since the site is not mobile friendly.

Additional context
isfdb.org has a lot of covers categorized by year and language. It's easy to find covers for your book, no matter what language.

[Sarat-1997]

@l3if3rik is the above cover source url work almost perfectly while searching and scanning all books?