Minimal fixes for xhtml front page RSS reader gadget

This makes RSS reader somehow usable for support request RSS.

One important think to keep in mind is that because of a bug in how URL characters are (not) escaped in the dialog to edit character is that editing the feed URL should be edited from knowledge pad module, and not directly from front page. Also this should be edited by clicking Edit button, not by pressing enter.

See merge request nexedi/erp5!1467