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
- Linux users often don't know that the C PoW is available and complain
it's slow. This will try to build it, and adds availability
notification in the status bar
- also, the updateStatusBar signal now allows emphasised notifications,
which will remain visible for a longer period of time and also
reappear if a status change happened in the meantime
