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.
Register functions which create each type of provider rather than the
provider types themselves so that the concrete types don't need to be
publicly exposed, and use a static list of providers rather than
registering them at runtime.
