Add image or icon in the definition

[ismailsunni]

Currently, we get the image or icon of a hazard / exposure in the wizard from something like this:

            item.setIcon(QtGui.QIcon(
                resources_path('img', 'wizard', 'keyword-subcategory-%s.svg'
                               % (h['key'] or 'notset'))))

This is not very neat. We should put the image resource in the definitions. By doing this we can get the image resource path from another module easily

This is a low priority though.