Consider splitting vs.c into pieces

[katajakasa]

Currently we handle all the following scenes in vs.c

• single player mode
• Two player mode with scene selection
• Tournament mode with only enemy insult
• Plug scene after tournament

The logic is a bit all over the place.

It might be a good idea to split this into pieces, like:

• vs_insults.c (for anything to do with insults)
• vs_plug.c (for tournament ending)
• vs_arena.c (for arena selection)

This will probably require some discussion.