Fix for Bootstrap 3.1+

In Bootstrap 3.1+, the .modal-backdrop class appeared on top of the .lightbox class because they both had z-index of 1040.  I modified the z-index of .lightbox to 1041 so that the lightbox behaves as expected.

Signed-off-by: Matt Libera <matthew@liberawebdesign.com>
Merge pull request #61 from mattlibera/master

Fix for Bootstrap 3.1+