Fix next-page bug

Due to waypoint-position being dependent on there actually being content
in the page, a little work-around is to do my own thing to detect when
the end of the page has been reached.
Change behaviour when adding a site

No longer is the existing site list modified to contain the new site and
then its items shown in the content pane... rather the site list and
content pane are both refreshed to show a mix of the previously existing
and new unread items.