I have difficulties installing pgAdmin's plugin PostGIS Layer Viewer. The official repository on GitHub gives this Web site for install procedure, then the former site gives this Web site for installing prerequisites.
I have well installed QGIS 2.8 through OSGeo4W. I have problems executing the python script that says from qgis.core import *, etc. See error message below:

I get the 'No module named...' message for either qgis.core, qgis.gui, PyQt4.QtCore and PyQt4.QtGui.
Could anybody help me?