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.
Add a new Project class which is responsible for everything related to
opening and closing audio, video, subtitles, timecodes and keyframes.
This pulls almost everything not directly related to playing audio/video
out of the audio and video controllers, pulls more crap out of
FrameMain, and happens to make things a little simpler in the process.
Thomas Goyne