Added logic to render only results in the visible frame (plus buffer on
either side).  a spacer div at the top of the search results acts as a
place holder for rows that have been removed as the user scrolls down.
At the same time, rows are appended to the bottom of the results as they
are added to the results collection.  As the user scrolls up, needed
rows are rendered and rows are removed from the bottom of the results
list (and the end of the results collection)