This adds a cleanup stage to remove database files for folders that no
longer exist on startup. Folder database files were already removed when
dropping a folder, assuming that the folder database had been opened at
that point. This won't be the case though when a folder is removed from
the config when Syncthing isn't running, or when a folder is dropped and
re-migrated in a restarted migration.
This changes the database structure to use one database per folder, with
a small main database to coordinate. Reverts the prior change to buffer
all files in memory when pulling, meaning there is now a phase where the
WAL file will grow significantly, at least for initial sync of folders
with many directories.
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Co-authored-by: bt90 <btom1990@googlemail.com>
Switch the database from LevelDB to SQLite, for greater stability and
simpler code.
Co-authored-by: Tommy van der Vorst <tommy@pixelspark.nl>
Co-authored-by: bt90 <btom1990@googlemail.com>
