Only populate the current needed story

This reduces scroll freezing in the other method, which I suspect was
caused by angular looping over all the divs look for contents.
Introduce a new Feed.NextUpdate field
Display bar tweaks
Fixed top navbar
Allow toggle of current story
Only alert if there's something to say
Story summaries
This is getting annoying...
Scroll to current story if needed
Allow j'ing down to last story
Also always fetch stories to either side of current