Demonstrate Qt QML with PyQt

Example how-to use Qt QML and Qt Quick Controls with PyQt.

I have a QtWidgets app.
I want to test these issues:
- will QML fix style issues on mobile platforms:  QtWidgets does not have native style on iOS.
- what widgets are missing in QML: form dialog and share sheet/button
- what architectures work (nesting QML in QWidget or vice versa)

This project has several qml files that demo:
- many built-in widgets (Quick controls)
- a model (a Component) defined in Python
- signals between QML and Python (back and forth)
- architectures: nesting QML inside a QWidget (but reverse is not possible in Qt Quick 2 in Qt 5 ? but is Qt Quick 1 still in Qt 5?

TODO:
- test iOS and Android for style conformance
- test whether QML dialogs nested in QWidget are full screen on mobile platforms
- Use pyrcc to put the qml in resources
- pyqtdeploy it

Quality: much cruft from failed experiments.  Probably fragile.  Not necessarily architecturally correct.