server: release all the resources on exit

Release all the resources including wlr_allocator, wlr_renderer,
wlr_backend and wlr_scene. This makes it a lot easier to detect memory
leaks with ASAN.

On wlroots side, the commit ce615a44 needs to be reverted to detect memory
leaks with EGL renderer.

src/main.c

@@ -228,11 +228,12 @@ main(int argc, char *argv[])
 
 	session_shutdown(&server);
 
-	server_finish(&server);
-
 	menu_finish(&server);
 	theme_finish(&theme);
 	rcxml_finish();
 	font_finish();
+
+	server_finish(&server);
+
 	return 0;
 }