imgconverter: add eq operation for Image class

This is used to check if the new icon is in any way different from the
old one and possibly avoid regenerating all of them.

core/imgconverter.py

@@ -191,6 +191,12 @@ expects header+RGBA on stdin. This method is invoked from qvm-imgconverter-clien
 
         return cls.get_from_stream(sys.stdin, **kwargs)
 
+    def __eq__(self, other):
+        return self._size == other._size and self._rgba == other._rgba
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
 def hex_to_float(colour, channels=3, depth=8):
     '''Convert hex colour definition to tuple of floats.'''