Added default language pack (en-gb)

admin/marketplace/api.php

@@ -0,0 +1,16 @@
+<?php
+// Heading
+$_['heading_title']    = 'OpenCart Marketplace API';
+
+// Text
+$_['text_success']     = 'Success: You have modified your API information!';
+$_['text_signup']      = 'Please enter your OpenCart API information which you can obtain <a href="https://www.opencart.com/index.php?route=account/store" target="_blank" class="alert-link">here</a>.';
+
+// Entry
+$_['entry_username']   = 'Username';
+$_['entry_secret']     = 'Secret';
+
+// Error
+$_['error_permission'] = 'Warning: You do not have permission to modify marketplace API!';
+$_['error_username']   = 'Username required!';
+$_['error_secret']     = 'Secret required!';