refs #650 Implement CAirportDataReader

* Add BlackCore::CAirportDataReader class
* Add cache traits for airport list
* Add corresponding WebReaderFlag
* Add CAirport::convertFromDatabaseJson()
* Add CApplication::headerFromNetwork() to handle HTTP HEAD method

src/blackcore/data/dbcaches.h

@@ -17,6 +17,7 @@
 #include "blackmisc/simulation/distributorlist.h"
 #include "blackmisc/aviation/airlineicaocodelist.h"
 #include "blackmisc/aviation/aircrafticaocodelist.h"
+#include "blackmisc/aviation/airportlist.h"
 #include "blackmisc/aviation/liverylist.h"
 #include "blackmisc/network/url.h"
 #include "blackmisc/countrylist.h"
@@ -108,6 +109,16 @@ namespace BlackCore
             //! Key in data cache
             static const char *key() { return "dbmodelreaderurl"; }
         };
+
+        //! Trait for airport list
+        struct DbAirportCache : public BlackMisc::CDataTrait<BlackMisc::Aviation::CAirportList>
+        {
+            //! Defer loading
+            static constexpr bool isDeferred() { return true; }
+
+            //! Key in data cache
+            static const char *key() { return "dbairportcache"; }
+        };
     } // ns
 } // ns