[BUGFIX] Add default value to TCA config (#157)

* [BUGFIX] Add default value to TCA config

Avoid error when copying page.

Fixes #111

* [TASK] Limit size of input field

As `maxitems` = 1 it's suitable to limit the
size of the field to `1` as well.

Fixes: #84

Configuration/TCA/Overrides/pages.php

@@ -38,6 +38,8 @@
                 'foreign_table' => 'tx_cartproducts_domain_model_product_product',
                 'minitems' => 0,
                 'maxitems' => 1,
+                'default' => 0,
+                'size' => 1,
             ],
         ],
     ];