Sunday Afternoons:  Slack Key Guitar Concerts.  Traditional Hawaiian slack key guitar and `ukulele concerts.  April 7 – Spirit of Slack Key; April 14 – Hawai`i’s Cowboy Music; April 21 – Slack Key Tour of the Islands; April 28 – Slack Key Story.  Tickets: $20 ($15 keiki/seniors).  The concerts are nahenahe - soft and sweet.  Slack key guitar and `ukulele in the real old style.  All traditional music with songs and stories of the islands, telling the history of this Hawaiian musical…