Do not run elevated by default (#884)

Make the runner not run as elevated by default. Add a setting for
"run PowerToys as elevated" and buttons to restart the process
with the different elevation levels.

src/runner/restart_elevated.h

@@ -0,0 +1,5 @@
+#pragma once
+void schedule_restart_as_elevated();
+void schedule_restart_as_non_elevated();
+bool is_restart_scheduled();
+bool restart_if_scheduled();