ACE Pro cutter system v2

THIS IS DEFINITELY A WORK IN PROGRESS!

This is a spring driven automatic filament cutter for use inside the Anycubic ACE Pro (1st version). I'd noticed when using the backup filament function that when a spool ran out, the kink often found at the end of the roll would cause a jam. This is another attempt to find a way to avoid that problem.

Current problems:
Spring and trigger - Balancing the tension needed to consistently cut filament, versus the pressure needed to release the trigger has been tricky. I think this needs a different trigger mechanism, but I haven't been smart enough to figure that out. Currently I've decided to make sure the filament consistently cuts, which means a heavier spring making it harder to trigger.

Also, I thought I'd made the base profile tight enough, but I was wrong. When the filament reverses in the ACE Pro, the cutter lifts and gets stuck behind the spool. I've added a hold-down bar that works, but is kind of ugly. There's got to be a more elegant w