Converter/ValueToPixmap.py: don't use cache with "Path" argument. refs #750
Converter/ValueToPixmap.py, Renderer/Pixmap.py: use cache for LoadPixmap inside ValueToPixmap converter, look for pixmap attribute inside Pixmap renderer and react on changes. refs #750
Components/Converter: add ValueToPixmap converter to convert a given path or language code to a pixmap pointer e.g. used by the pixmap renderer. refs #750