Store the data in vectors rather than AssFiles since even an intrusive
linked list has comically high memory overhead. Cuts memory usage of a
full undo stack with 15k lines by 65 MB for 32-bit and 130 MB for
64-bit. Also roughly halves how long it takes to copy the file for the
undo stack, and makes undo/redo a bit faster.
Don't delete the old copy of the file until after the new version is
committed to avoid a use-after-free when code tries to do things with
the active line in a COMMIT_NEW handler, as just trying to avoid doing
that hasn't really worked out.
For whatever reason this was sometimes being done after the commit,
which resulted in a lot of code only working by coincidence when the
grid commit handler happened to be the first one to be called.
Relying on TextFileReader to do the charset detection results in the
user being prompted to pick a charset twice when it can't be
auto-detected, since the result from trying to open the subtitles as
timecodes was not being reused.
Closes#1512.
Add SubsController, which deals with things like what subtitle file is
currently open, rather than the contents of the current subtitle file.
Move the rest of the relevant logic from FrameMain there in addition to
all of the stuff from AssFile.
