Replace PyQt5 with qtpy

[ElpadoCan]

Description:

Replace PyQt5 dependency with qtpy, which provides support for PyQt5, PyQt6, PySide6, PySide2 using the Qt5 layout.

For example instead of from PyQt5.QtCore import Qt we can just do from qtpy.QtCore import Qt while having any of the Qt bindings library installed.

This is particularly useful on Apple Silicon CPUs where it could be easier to install PyQt6 instead of PyQt5.

To do:

• Replace all imports from PyQt5. with from qtpy.
• Correct imports QtCore.pyqtSignal, QtCore.pyqtSlot and QtCore.pyqtProperty (available on PyQt5/6) since they are exposed as QtCore.Signal, QtCore.Slot and QtCore.Property, respectively.
• Remove PyQt5 dependency and add additional extras_require with pyqt5 (to use PyQt5), pyside2 (to use PySide2) pyqt6 (to use PyQt6) pyside6 (to use PySide6).`
• When running acdc for the first time, if a GUI library is missing, ask the user (in the terminal) which library they want to install. Default to PyQt5 on Windows and PyQt6 on Apple Silicon Mac.