SPRINGFIELD — The storage-room merchants’ desk where President-elect Abraham Lincoln penned his first inaugural address, beseeching southern states to recall the “mystic chords of memory” and invoke “the better angels of our nature” to circumvent the Civil War, was unveiled by Illinois officials Thursday after a painstaking restoration to its 1850s splendor.The walnut-and-poplar hulk is displayed in the library atrium of the Abraham Lincoln Presidential Library and Museum in downtown …