Add route filter screen with airport name lookup

src/airport_lookup.h

@@ -13,5 +13,9 @@ namespace AirportLookup {
         double lat = 0;
         double lon = 0;
     };
-    Nearest findNearest(double lat, double lon);
+Nearest findNearest(double lat, double lon);
+
+    // Looks up an airport name by ICAO code (e.g. "EDDF" -> "Frankfurt Main")
+    // from the airports CSV on the SD card. Returns empty string if not found.
+    String findName(const char* icao);
 }