FreeBSD support

  Summary of the changes:

    - "${apache::conf_dir}/Includes" as $apache::confd_dir for FreeBSD,
    - "${apache::conf_dir}/Modules" as $apache::mod_dir FreeBSD,
    - "${apache::conf_dir}/Vhosts" as $apache::vhost_dir FreeBSD,
    - added $root_group, $apache_package, $server_root to
      apache::params,
    - added $loadfile parameter to apache::mod,
    - added $mime_support_package parameter to apache::mod::mime class,
    - apache::mod::mime installs $mime_support_package package,
    - added $magic_file parameter to apache::mod::mime_magic class,
    - added 'default_confd_files.pp', and confd template infrastructure to
      allow putting some files under conf.d/ (Includes/ under FreeBSD) by
      default (FreeBSD's apache22 installs Includes/no-accf.conf for
      example but puppet normally would purge it afterward),
    - touched documentation (README.md),
    - other (minor) changes and additions,
FreeBSD support enhanced

  Summary of changes:

    - properly react to changes done by apxs when it activates apache
      modules, so httpd.conf gets reverted to our desired state after
      a module is installed (FreeBSD),
    - install apache port (FreeBSD) appropriate for the MPM module
      selected by user,
    - more MPM modules under (FreeBSD),
    - new class apache::package to intelligently install appropriate
      apache package (depending on mpm_module chosen),
    - elaborated $apache::params::mod_packages list,
    - other fixes,