EMI: Refactor ranges for sound volume

- LUA code uses a range of 25 .. 100
- residualvm engine uses a range of 0 .. Audio::Mixer::kMaxChannelVolume
- do all conversion in lua_v2_sound.cpp
- use LUA range when saving/restoring values in registry
  (since it is only read/written via LUA code)
- all other parts of the engine will solely use the engine internal
  range
GRIM/EMI: Set move volume to SFX volume setting