Major restructure, bundle blobs

This commit also breaks the repository format.

test/backend.go

@@ -52,7 +52,6 @@ func SetupKey(t testing.TB, s *server.Server, password string) *server.Key {
 func SnapshotDir(t testing.TB, server *server.Server, path string, parent backend.ID) *restic.Snapshot {
 	arch, err := restic.NewArchiver(server)
 	OK(t, err)
-	OK(t, arch.Preload())
 	sn, _, err := arch.Snapshot(nil, []string{path}, parent)
 	OK(t, err)
 	return sn