Add new icon for webservice refresh

The web-refresh icon is used on the Journal expanded-entry toolbar. It
is used as a button to contain a palette of refresh buttons used by
webservices.

This button is used in journaltoolbar.py as per [1].

The relevant feature request is [2].

[1] https://github.com/sugarlabs/sugar/pull/62
[2] http://wiki.sugarlabs.org/go/Features/Web_services