Lay the station form out the way N1MM lays it out

The dialog now carries N1MM's fields in N1MM's order, with the labels to
the left of the boxes and the tip text at the top right. New fields in
StoredStation: the address, the licence class, the position, the radio,
the antenna and the email address.

The grid square and the position fill each other in, as they do in N1MM.
Which box has focus decides the direction, because TextChanged arrives
too late to tell a typed edit from a programmed one.

The fields N1MM's form does not have are gone from it. Continent and the
country prefix are looked up from the callsign after Ok; the rest keep
the value they had.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/Nonemm.Core.Tests/GridSquareTests.cs

@@ -43,4 +43,15 @@ public class GridSquareTests
         Assert.True(GridSquare.TryParse("JP90", out GridSquare north));
         Assert.Equal(0, south.BearingTo(north), 6);
     }
+
+    [Theory]
+    [InlineData("JN88md")]
+    [InlineData("FN31pr")]
+    [InlineData("AA00aa")]
+    [InlineData("RR99xx")]
+    public void LocatorOfASquareCentreIsThatSquare(string locator)
+    {
+        Assert.True(GridSquare.TryParse(locator, out GridSquare grid));
+        Assert.Equal(locator, GridSquare.From(grid.Latitude, grid.Longitude));
+    }
 }