PyPi v1.4.0

Major clean-up and streamlining:

• Using qtpy library instead of my own Qt5/6 mechanism
• Changed all string formatting to f-strings
• Extended type hinting and checking
• Made demos uniform and passing qdev arguments to MainWindow now
• Individual source files now follow the PyPi package version
• Resolved nearly all Pylint / Pylance warnings
• Removed Python 3.6 support