Added support for intro sound configuration/ Reduced line count

Added intro_sound to sh_options and changed cl_kernel to reflect the
changes.
intro_sound reflects the configuration available for intro_image and
menu_music

Reduced line count in sh_entity, from Chessnut's commit, but with proper copyright.
https://github.com/Chessnut/Clockwork/commit/2c86d0327072678f49555bf80132ea42d7b9a099