CGE2: Distinguish SFX from speech when playing sounds.

Now the sound options of ScummVM are taken into account when playing these two types of sounds. Until now, everything was considered SFX sound.
CGE2: Remove redundant default labels.
CGE2: Repair/rename checkSoundHandle().
CGE2: Implement snTrans() and snPort().
CGE2: Remove handling of unused opcodes.
CGE2: Remove the unused opcodes.
CGE2: Fix typo in SETREF's comment.
CGE2: Remove more unused opcodes.
CGE2: Remove kCmdDim and kCmdStep and connected code.
CGE2: Fix kCmdWalk's comment.
CGE2: Rearrange _commandText[]'s content.