[#128] metabase: Implement Delete method

Implement Delete method on DB structure that adds deleted addresses to
tombstone index. Do not attach addresses from tombstone index to Select
result. Return error from Get method if address is presented in tombstone
index.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/metabase/select.go

@@ -67,6 +67,11 @@ func (db *DB) Select(fs object.SearchFilters) ([]*object.Address, error) {
 				return nil
 			}
 
+			// check if object marked as deleted
+			if objectRemoved(tx, k) {
+				return nil
+			}
+
 			addr := object.NewAddress()
 			if err := addr.Parse(string(k)); err != nil {
 				// TODO: storage was broken, so we need to handle it