Add apache::conf

* I moved the bulk of code in apache::site to a new resource type,
  apache::conf, which can manage either a sites-{enabled,disabled} config file
  or a conf-{enabled,disabled} config file.
* I made apache::site be a thin wrapper around that.
  (Why keep apache::site at all? Because it's clearer and neater than
  "apache::conf { '..': type => 'sites', ... } ".)
* Since the module now manages files in conf-enabled as well as sites-enabled,
  declare the former directory too and manage it in the same way.
* conf-enabled/* is Ubuntu 13.10+; prior releases use conf.d/*. So provide a
  small shim for older versions, in keeping with the philosophy of seamless
  cross-compatibility.
* Also remove unused service_enabled param and .gemfile, .gitignore,
  .travis.yml files.

Change-Id: I5bf6186d70e47cfc04e9d78da145d5f82b08504d