Added a new form to display the GPLv3 license for the project.

Resolves issue #6.

AboutBox1.cs

@@ -106,5 +106,11 @@ namespace PDF_Merge
         {
             this.Close();
         }
+
+        private void labelCopyright_Click(object sender, EventArgs e)
+        {
+            LicenseForm LicenseWindow = new LicenseForm();
+            LicenseWindow.Show();
+        }
     }
 }