Definitions: Automatically parse translated MAPINFO defs during game init

To do this 100% correctly would involve Doomsday Script. For now this
translation task is scheduled in readAllDefinitions() and performed
for all supported games.
libdoomsday|DED: Music definitions support the 'Mods' directive

As of this commit all Hexen based games are again playable.

Todo: The way Music defs are integrated with Hexen prevents the CD
track numbers defined in MAPINFO from being applied as expected. Is
the "current" Map Info definition mechanic still the best solution?