Add refresh-translatable-pages.php script

Change-Id: Iac3f1aabea90fad0a30eb6805e14d0a21ab12926
Small comment fixes

* translatetoolkit has been replaced with TTMServer long ago
* headers per RFC to localisation team
* removed no-op cache purging

Change-Id: Ifcf17393d04cb995fb6105cb835deea0386c3245