Register book-metadata-provider services by address, with no code change per
provider; Settings lists ready-made ones to install. Ranking prefers a record of
the book's own medium. LubimyCzytac moves out to its own provider and Aladin,
whose API closes, is retired; their ids stay. Adds migrations 0129 and 0130.
See docs/METADATA_PROVIDERS.md.
Ref #1405
neon