Add the rest of the major contests, .udc files and the registry

ARRL DX, IARU HF, Sweepstakes, RTTY Roundup, NAQP and general logging join
CQ WW and CQ WPX. The Cabrillo QSO line is now built column by column by the
contest, because Sweepstakes puts the callsign after the serial number where
everyone else puts it first.

User-defined contests read the subset of N1MM's .udc settings that covers the
exchange, the dupe rule, points and up to three multipliers.

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

src/Nonemm.Contests/Contest.cs

@@ -14,7 +14,9 @@ public interface Contest
     /// The name the sponsor's Cabrillo header asks for.
     string CabrilloName { get; }
 
-    IReadOnlyList<ExchangeField> ExchangeFields { get; }
+    /// The boxes the entry window shows. ARRL DX and others ask for a
+    /// different exchange depending on where the operator is.
+    IReadOnlyList<ExchangeField> ExchangeFieldsFor(StationInfo me);
 
     /// Up to three names, in the order the score summary shows them.
     IReadOnlyList<string> MultiplierNames { get; }