Python qt: version notes

New major releases of Qt come with breaking changes. I've only been working with Qt through one transition, but as I encounter new changes, I'll record them here.

If you are concerned about compatibility, I've noticed that QtCore, QtGui, QtWidgets are usually available everywhere. Other modules are sometimes installed separately, and take special note of modules like phonon which do not have a prefix of Qt - They are often written/maintained by third party groups, and mileage varies when it comes to long-term support.

Qt4-Qt5

• QWidgets/QApplication moved from QtGui to a new module: QtWidgets
• toplevel import: QtWebKit moved to QtWebEngine