start schema version 7 (#155)

This isn't yet any different than schema version 6.

server/db/upgrade/v6_to_v7.rs

@@ -0,0 +1,10 @@
+// This file is part of Moonfire NVR, a security camera network video recorder.
+// Copyright (C) 2021 The Moonfire NVR Authors; see AUTHORS and LICENSE.txt.
+// SPDX-License-Identifier: GPL-v3.0-or-later WITH GPL-3.0-linking-exception
+
+/// Upgrades a version 6 schema to a version 7 schema.
+use failure::Error;
+
+pub fn run(_args: &super::Args, _tx: &rusqlite::Transaction) -> Result<(), Error> {
+    Ok(())
+}