Make Photos Vis Unbroken

If the photos being displayed fit on one line, they are displayed horizontally with standard margins.
If the number of photos being displayed extends onto multiple lines, Figure out the maximum number of photos per line, display them with equal margins, and add half the difference between the div width and the width of the n photos (plus margins) to "center" the n equidistant photos.  The next row of photos then lines up with the previous row.  Resizing the windows changes the number of photos per line, but preserves the above properties.  Addresses issue #1557