WIP: selecting match added

src/PlayOffMatchSelectedEventArgs.cs

+namespace TournamentManager
+{
+    public class MatchSpecsSelectedEventArgs : CbItemSelectedEventArgs
+    {
+        public string SelectedMatch { get; }
+        
+        public MatchSpecsSelectedEventArgs(string itemName, string selectedMatch)
+            : base(itemName)
+        {
+            SelectedMatch = selectedMatch;
+        }
+    }
+}
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