Show active and available pilots in air wing view.

https://github.com/dcs-liberation/dcs_liberation/issues/276

qt_ui/windows/AirWingDialog.py

@@ -39,6 +39,10 @@ class SquadronDelegate(TwoColumnRowDelegate):
             )
         elif (row, column) == (1, 0):
             return self.squadron(index).nickname
+        elif (row, column) == (1, 1):
+            squadron = self.squadron(index)
+            available = len(squadron.available_pilots)
+            return f"{squadron.size} active pilots, {available} available"
         return ""