The playlist macros set the music list twice, once before the
story screen and again in prestart, but the order of tracks is different.
This means that the track order at the titlescreen and in the lobby is now the same
as the track order in a scenario using the default playlist, which previously was not the case.
Similarly, the track order in the editor is now the same as the track order
in a scenario using the full playlist.
Whether that actually matters? I have no idea. I doubt it.
In any case, as of this commit, there are no schema validation errors
at the title screen, when entering the MP Create screen, or in the map editor.
...so that the editor doesn't need to set the MULTIPLAYER symbol. Also
made the editor include the UMC campaigns dir, so that UMC can make
their custom terrains available to the editor.
