Operation Node refactor

[radudum10]

• operation_node.py classes are now in separated files and some of them have been completely refactored.
• I have fixed the dependencies between the classes.
• This is currently still in progress, review and testing are welcome!

[razvand]

@radudum10 , this requires rebasing.

This is still WIP so commits and commit messages are not that relevant now. But when getting closer to merging the PR, please be sure that:

• commit messages are well written: see instruction here: https://chris.beams.io/posts/git-commit/
• commit messages are complete and atomic: one commit is one functionality; there won't be a commit with two ideas inside it, or an idea spread across multiple commits