[mini-project][RFC] builtin map merger/converter

[TsFreddie]

More detailed design TBA. But the general idea is that a gamemode should be able to describe how a map is modified before serving it to players.

I think in most cases providing a "template map" is enough where the map merger sandwich the loaded map with template layers before and after the game layer in template map.

Not sure if we need any interface to modify maps programmatically. (I'd prefer not having a map compositing interface so it is less work XD)

And obviously, #10 needs to happen before we can do this one.