HHVM FastCGI

Work in progress, opening PR for review. Seems to work though - kind of, maybe, sometimes, on my machine...

Branch is based on https://github.com/till/easybib-cookbooks/pull/344 because it depends on HHVM, obviously.

Still needs:
* [ ] deploy recipe (or maybe we can add that later)
* [x] cleanup
* [x] tests / chefspec / whatever (well, somewhat)
* [x] sanity testing re: config file locations / content
   * [x] I think I'll need to add an init.d script to tell hhvm to use the `php-fcgi.ini` in server mode
   * [x] memory limit may need to get increased ~~also: it seems to ignore the 512MB limit (ini_get says 1024)~~
   * [x] neither display errors nor the error log seem to work
   * [x] config file names should go into attributes, too
Please add a raise "TODO" or fatal "TODO" here, to make sure this does not end up in debugging hell on opsworks :)