QtPy is a compatibility layer which allows to use the code written for
PyQt5 with any python Qt binding: PyQt4, PyQt5, pyside or pyside2.
Main differences in PyQt5:
- all widget classes are now in QtWidgets package, not QtGui;
- QString obsoleted by unicode (sip API 2);
- changed the way of signals connection.
Closes: #1191
Zooming in message body view / compose works in single steps
irrespective of wheel sensitivity, and info about zoom level is
displayed in percent rather than font pixel size.
