Added UseYearGroup fonctionnality

src/tp04/UseYearGroup.java

+package tp04;
+
+public class UseYearGroup {
+    
+    public static void main (String[] args) {
+        
+        YearGroup yg = new YearGroup();
+
+        yg.addStudent(new StudentAbs("Alice", "A.", 18, 2));
+        yg.addStudent(new StudentAbs("Bob", "B.", 3, 2));
+        yg.addStudent(new StudentAbs("Carlos", "C.", 6, 18));
+        yg.addStudent(new StudentAbs("Dimitri", "D.", 4, 19));
+
+        yg.validation();
+
+    }
+
+}
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