strife: Fix default music volume to match Vanilla.

Strife's default music volume is 13 as opposed to Doom's value of 8.
This was apparently not changed during the development of Chocolate
Strife. Thanks to Alexandre-Xavier for noticing this and providing the
correct value (bug #347).
setup: Make default sound volumes match Vanilla.

Doom, Heretic, Hexen and Strife have different default SFX and music
volumes. Make sure the setup tool sets the appropriate default when
creating a new configuration file.

Thanks to Alexandre-Xavier for reporting this and providing the
correct defaults. This fixes #347.