added virtual verify member function in entry class

src/classes/aircraft.h

@@ -28,7 +28,7 @@ class aircraft : public entry
 {
 using entry::entry;
 public:
-    void verify();
+    bool verify() override;
 };
 
 #endif // AIRCRAFT_H

src/classes/flight.h

@@ -28,7 +28,7 @@ class flight : public entry
 {
     using entry::entry;
 
-    bool verify();
+    bool verify() override;
 };
 
 #endif // FLIGHT_H

src/classes/pilot.h

@@ -24,7 +24,7 @@ class pilot : public entry
 {
     using entry::entry;
 public:
-    void verify();
+    bool verify() override;
 };
 
 #endif // PILOT_H

src/database/entry.h

@@ -43,6 +43,8 @@ public:
     bool remove();
     bool exists();
 
+    bool virtual verify();
+
     // Debug functionality
     void print();
     QString debug();