Add support for registering additional save and load steps

Also renamed the reset steps to make it more clear what their use is.

src/advanced-scene-switcher.cpp

@@ -334,7 +334,7 @@ void SwitcherData::ResetForNextInterval()
 	// Core reset functions
 	ClearWebsocketMessages();
 	// Plugin reset functions
-	for (const auto &func : resetForNextIntervalFuncs) {
+	for (const auto &func : resetIntervalSteps) {
 		func();
 	}
 }