Refactor main menu

[vkbo]

Summary:

This PR:

• Moves the linking of menu action objects to the main GUI to where the actions are defined instead of pulling them in a utility function.
• Adds a new qtLambda function to be used for Qt signals when passing custom arguments. This strips the original arguments, and properly sets a None return value. For Qt6, the linter will otherwise complain about this. This also solves the problems of generating slots using lambdas in for loops. Python will by default not generate new lambdas for each cycle, so it has to be tricked. Otherwise, all elements in the loop will end up with the last lambda generated.

Related Issue(s):

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed