add dedicated stopAll()

should not change abi

solanaceae/plugin/plugin_manager.hpp

@@ -47,6 +47,9 @@ struct PluginManager {
 
 	bool add(const std::string& plug_path);
 
+	// stops, but does not remove/unload, all plugins
+	void stopAll(void);
+
 	// returns the minimum time until next call is wanted in seconds
 	float tick(float delta);
 	float render(float delta);