chore: switch database engine to sqlite (fixes #9954) (#9965)

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>

lib/versioner/external.go

@@ -41,7 +41,7 @@ func newExternal(cfg config.FolderConfiguration) Versioner {
 
 	s := external{
 		command:    command,
-		filesystem: cfg.Filesystem(nil),
+		filesystem: cfg.Filesystem(),
 	}
 
 	l.Debugf("instantiated %#v", s)