QWidget-based class used for viewing QPixmaps
Based on python implementation (qpixmapwidget.py) found at http://pydoc.net/Python/taurus/2.1.0/taurus.qt.qtgui.display.qpixmapwidget/ http://www.tango-controls.org/static/taurus/v300/doc/html/devel/api/taurus/qt/qtgui/display/_QPixmapWidget.html