Worldmaps: support switching music without scripts

[maxteufel]

Add a way to switch music in worldmaps without using scripts. This will be necessary for the "merged" Icy Island and Forest Island worldmap in a later release.

[Karkus476]

@maxteufel What's wrong with scripting?

[maxteufel]

@Karkus476 Scripting requires additional work to track state during restarts. Also without proper implementation it might result in issues similar to the sprite change one.

[Karkus476]

@maxteufel Fair enough, but we do need to get to the point where everything is scriptable, so that level designers have complete control over the level. A secure way to preserve data through restart might be worth creating?

[maxteufel]

@Karkus476 I believe that is a different issue (open a new one, I guess?) and will require careful planning and discussion.

[Rusty-Box]

An idea could be using an object similar to the special tile where you can select a new music that plays once players touch this object on a worldmap. The already existing special tile could be used for that as well, I think.