Keep track of which lines are displayed on the current video frame so
that video seeks only have to repaint the grid when the set actually
changes. Speeds up video playback on non-fbf stuff by ~15%.
The relative order of the on-file-load logic matters, so signals don't
work very well for it. Doing it all explicitly in Project fixes a bunch
of inconsistent issues related to restoring saved state.
Closes#1759.
Remove it from the script info section and put it in its own section
that isn't tracked by undo and make it not stringly typed. Removes the
need for the gross hack where changes are slipped in just before saving
to circumvent the undo system, cuts down on the uses of string literals
to identify fields, and probably improves performance a little.
The grid needs to be able to map AssDialogue * to a row number, and just
storing it in the AssDialogue is nearly strictly better than a std::map
mapping events to rows. Probably will be of use elsewhere as well.