Various Cuiman GUI enhancements

[forman]

In this PR:

• Added preliminary output GUI to the main panel in cuiman.gui.panels. Only shown, if multiple output values are used. The UI is still experimental and subject to change.
• Refactored panels in cuiman.gui.panels package to follow MVVM (Model–View–ViewModel) style.
• Allowed for making inputs "advanced" and initially hiding advanced inputs in the UI. Added a switch to show advanced inputs. (Experimental)
• No longer showing "No job selected" in the GUI client's main panel. If no job info given, the job info panel is now hidden.
• Removed persistent error message in GUI client's job info panel.

Closes #36

Checklist (strike out non-applicable):

• Changes documented in CHANGES.md
• Related issue exists and is referred to in the PR description and CHANGES.md
• Added docstrings and API docs for any new/modified user-facing classes and functions
• Changes/features documented in docs/*
• Unit-tests adapted/added for changes/features
• Test coverage remains or increases (target 100%)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!