Bug866810 favicon in django

This change also contains a change of the `favico.ico` file. It used to be a PNG image (e.g. `PNG image data, 16 x 16, 8-bit/color RGBA, non-interlaced`) despite it's file extension. 

Now it's a proper .ico file (e.g. `MS Windows icon resource - 1 icon`)

It's now also 2547 bytes smaller :)