replace php RSS parsing code by js/jquery

The goal is ultimately to get rid of calls to sfWebBrowser(), as this
blocks php when the remote resource is slow/unavailable.

No fancy layout yet, just a working prototype.
use an IIFE to avoid polluting global namespace
indentation consistency
use $.get().done()
meta rss: restore fancy layout
meta rss: display message by default, replace by content if there is some
inline JS metaengine rss parser
meta rss: nicer waiting/error messages
Merge branch 'get-rid-of-sfFeedPeer'