Added basic widget RSFeedWidget for showing feed items in a QTreeWidget as replacement for the QScrollArea.
- Use sort of QTreeWidget
- Filter items
- Open/collapse selected item with +/-
- Remove selecteds item with dselete key

git-svn-id: http://svn.code.sf.net/p/retroshare/code/trunk@7478 b45a01b8-16f6-495d-af2f-9b41ad6348cc