Adding RDF Editor Icon to the application

Task to solve

As an user, I want to see the Icon of RDF Editor on the Taskbar and on the top left corner of the app.

Goals

• Set the Icon in MainWindow.
• Show the Icon on the Taskbar.

Proposal

It should be possible to set the Icon in MainWindow with the Widget.setWindowIcon method which MainWindow inherits. For the icon appearance on the task bar the method QGuiApplication.setWindowIcon (which QApplication inherits) should be used in app.py