Improve handling of feeds with missing data

Improve handling of feeds with missing data

Previously the description was used in the treeview if the title
was not present, however this is not possible in some cases, as
it may contain markup.
The the RSS code is changed so now if there is no title, the
description is used as the title, but with the html stripped from
it. We also have to consider that some description elements may
simply contain an html tag (and therefore no text). In that
case the URI is used as the title.