Added default language pack (en-gb)

admin/marketplace/extension.php

@@ -0,0 +1,9 @@
+<?php
+// Heading
+$_['heading_title'] = 'Extensions';
+
+// Text
+$_['text_success']  = 'Success: You have modified extensions!';
+$_['text_list']     = 'Extension List';
+$_['text_type']     = 'Choose the extension type';
+$_['text_filter']   = 'Filter';