(Etherpad 1.4.0) Bump Etherpad version and add ep_page_view plugin

This has been packaged and is available here:

https://s3.amazonaws.com/oae-releases/etherpad/1.4/etherpad-1.4.0_node-0.10.28.tar.gz

I've deployed it on the performance testing environment for now and it looks good. Let's bug-bash it soon and then release it.