Add translations for OmniPrice module in French and Italian, and update upgrade scripts

- Added French translations for the OmniPrice module (fr.php).
- Added Italian translations for the OmniPrice module (it.php).
- Created empty Dutch translation file (nl.php).
- Implemented upgrade script for version 1.1.11 to update configuration for showing real discount.
- Implemented upgrade script for version 1.2.0 to update configuration for indexing inactive products.
- Implemented upgrade script for version 1.2.3 to update configuration for ignoring non-EU countries.

modules/gm_omniprice/upgrade/upgrade-1.2.3.php

@@ -0,0 +1,10 @@
+<?php
+if (!defined('_PS_VERSION_')) {
+    exit;
+}
+
+function upgrade_module_1_2_3($object)
+{
+    Configuration::updateValue('GM_OMNIPRICE_IGNORE_NON_EU', false);
+    return true;
+}