Add composer to the stack

[pavelito]

No description provided.

[evanplaice]

The composer install can be simplified to one command (ie moving the file is not required)

  exec { 'download-composer':
    command => 'curl -sS https://getcomposer.org/installer | sudo php -- --install-dir=/usr/local/bin --filename=composer'
  }

Also, sudo is required to write to /usr/local/bin