Move most karaoke parsing/serializing/editing code to AssKaraoke rather
than being scattered all over the place, and add much better support for
non-karaoke override tags and comments.
Add a karaoke timing controller.
Redesign the karaoke syllable split/join interface to have a single mode
from which both splitting and joining can be done rather than separate
split and join modes.
Only show the karaoke split/join bar when karaoke mode is enabled.
Closes#886, #987, #1190.
Originally committed to SVN as r5613.
