[FIX] website: partial revert of 6207644

Before this revision, it was possible to use the
`/website/image` controller using kwargs only
e.g.
`/website/image?field=datas&model=ir.attachment&id=718207`

After, it's no longer possible.

It was assumed `/website/image` without any argument
in the route itself (`<xmlid>`, `<field>`, ...)
could simply never be called,
but this is not the case.

We therefore restore it by retro-compability purposes.

addons/website/controllers/main.py

@@ -433,6 +433,7 @@ class Website(openerp.addons.web.controllers.main.Home):
         return request.registry['website']._image_placeholder(response)
 
     @http.route([
+        '/website/image',
         '/website/image/<xmlid>',
         '/website/image/<xmlid>/<int:max_width>x<int:max_height>',
         '/website/image/<xmlid>/<field>',