Eoin O'Neill authored May 04, 2022 and Amy spark committed May 19, 2023

- Renamed playback range classes and methods to better reflect actual use.
- We now use a custom Krita module for MLT name "ranged" that restricts seeking
to a frame range in the way Krita expects.
- Hooked up playback range "end" and "start" GUI to appropriate MLT methods.
- Rewrote producer initialization so that it always happens within the scope of
one method, making it easier to manage.

And probably some more.