Sound export improvements

[NicknineTheEagle]

• Changed UE3 PS3 MSF sound extension from .mp3 to .msf. This is the real extension of this format as seen in numerous PS3 games.
• Use FileType variable for extension as default when exporting USound since this var contains source file's extension.
• Added "drop remaining data" hack from other sound classes to USound. Fixes Harry Potter and the Philosopher's Stone and probably some other games.
• Added .umx to package extensions list.
• Added UMusic class. It's typically used for storing tracker music in early games like Unreal, appears to be identical to USound when serialized so I added it as an alias.
• Added mutated version of USound from Harry Potter and the Chamber of Secrets.
• Added user option to toggle converting UE3 XMA to RIFF when exporting. vgmstream supports raw UE3 XMA so this is a viable export option now.