Previous iteration used some "magic code" that added clips automatically to the
timeline. This was functional but ultimately outside of the undo commands'
control meaning nodes could be infinitely added and abandoned. This makes the
add process part of the undo command which means it's all undoable as the user
would expect.
Fixes recurring design issue that the Blocks were a frequent exception to the
DAG concept. The Blocks connecting to each others inputs/outputs while not
necessarily being "dependent" on each other to produce an image continually
causes issues while trying to create a rendering code path. This redesign
should provide a more "directed" approach to the directed acyclic graph.
Since we're now working with a separate proxy copy of the original node graph,
if the user changes a parameter in one of those nodes (triggering an
InvalidateCache signal), the values in our copied graph need to be updated
with these new values too.
itsmattkc