refs #707, refactoring geo interfaces

* added compare functions (also to ATC list)
* renamed to relative position, e.g. station.setRelativeDistance
* delegate set/get/compare to correct interface

src/blackmisc/comparefunctions.cpp

@@ -38,5 +38,9 @@ namespace BlackMisc
             return a < b ? -10 : 10;
         }
 
+        int compare(const QDateTime &a, const QDateTime &b)
+        {
+            return Compare::compare(a.toMSecsSinceEpoch(), b.toMSecsSinceEpoch());
+        }
     } // ns
 } // ns