QOL Improvements, including PEP8 compliance, cross platform support and more

[JaimeFlorian27]

This was the first tool I released and coming back to review the code was a painful experience, it's time to give it a well-deserved refactor:

• PEP8 compliance.
• Better separation of concerns (UI VS core).
• Abstracting DCC logic for future extension.
• unit and integration testing.
• no more pre-compiled UI with pyside2-uic, using .ui directly.
• use of Qt.py to allow compatibility with multiple Qt bindings for Python.
• Not version controlling ffmpeg's binary (WHAT WAS I THINKING?? AND IT'S IN THE LIB DIRECTORY? hehe)
• ? CI / CD for automatic build? It will be needed if I want nontechnical artists to be able to download and use it immediately without installing stuff on their side (such as ffmpeg).
• Threading (or multiprocessing) if necessary