(db upgrade to v22.00)
`scan_kind` identifies the library "scanner" component that created the
item and is responsible to keep it up to date (rescan).
The library update now supports passing a `scan_kind` to update only the
items of one particular "scanner". This allows e. g. to only update the
item from the Spotify library or only update the RSS feeds.
The OwnTone database is upgraded to v22.00 and the `scan_kind` columns
in `files`, `playlists`, `directories` are identified by:
1. Check if item is part of a RSS playlist (podcast RSS feed), they
belong to the "rssscanner"
2. Check if item has a Spotify `virtual_path`, they belong to the
"spotifyscanner"
3. Remaining items belong to the "filescanner"
Select use of either libspotify or librespot-c as streaming backend via config
option.
librespot-c (renamed/improved spotifyc) impl has the following:
- sync interface
- seek support
- honor bitrate config, set client and thread name
- use web access token with "streaming" scope for login
- fix issue with podcast playback
Also say goodbye to file-based Spotify login.
