Converting "next" / "prev" links in slideshow to use arrow icons from FontAwesome (using actual images, though, for IE 7 support)

Signed-off-by: Matt Bernhardt <mjbernha@mit.edu>
Changing front page tabs to use user-supplied slugs (fields need to be defined via Custom Fields module)

Signed-off-by: Matt Bernhardt <mjbernha@mit.edu>