Module assets should not be sent a far-future expires header

Modules should no longer include either the application version number in the URL, or include a far-future expires header. Instead, module requests and response should support HTTP Etags (http://en.wikipedia.org/wiki/HTTP_ETag).

The reasoning behind abandoning the application version number is that it relies on the developer to know when to change the version number (well, basically on every redeployment), and it invalidates all assets (this it the case in Tapestry 5.3).