Added default language pack (en-gb)

admin/extension/total/sub_total.php

@@ -0,0 +1,15 @@
+<?php
+// Heading
+$_['heading_title']    = 'Sub-Total';
+
+// Text
+$_['text_extension']   = 'Extensions';
+$_['text_success']     = 'Success: You have modified sub-total total!';
+$_['text_edit']        = 'Edit Sub-Total Total';
+
+// Entry
+$_['entry_status']     = 'Status';
+$_['entry_sort_order'] = 'Sort Order';
+
+// Error
+$_['error_permission'] = 'Warning: You do not have permission to modify sub-total total!';