Confused Carols - 12 Dec 23 Update

Found a few more pieces of Christmas music in the public domain beyond the hymn-ish set I started with and added 10 new puzzles.  2 easy puzzles (Ding Dong Merrily on High, Deck the Halls); 5 medium puzzles (Here We Come A-Caroling/Verse, The Holly and the Ivy, In Dulci Jubilo, Jingle Bells, Up on the Housetop); 3 hard puzzles (Here We Come A-Caroling/Chorus, O Christmas Tree, Pat-a-Pan).

Added a "Stop" button to the title bar that stops any currently playing music.  This allows you to skip the full play through after find the solution, or return to solving the puzzle faster after you've heard what you needed to.  The "Back" button has also been updated with this behavior so the music from an old puzzle won't continue to play after you've abandoned the puzzle.

Fixed a bug where completion of "O Come, O Come, Emmanuel (Verse)" was not correctly tracked.