Added delete method in GroupService

Signed-off-by: Marcin Woźniak <y0rune@aol.com>

buisnesslogic/src/main/java/com/plannaplan/services/GroupService.java

@@ -28,6 +28,10 @@ public class GroupService {
         this.repo.save(group);
     }
 
+    public void delete(Groups groups){
+        this.repo.delete(groups);
+    }
+
     public int getGroupsAmmount(){
         return (int)this.repo.count();
     }