invenio-setup-prerequisites: Ubuntu 14.04 support

* Checks if the string 'Ubuntu 14.04' is contained in /etc/os-release
* Adds function ubuntu1404_install_packages: it is based on debian_install_packages but it does not install openoffice.org (it has no installation candidate)
* Adds function ubuntu1404_configure_mysql: it calls debian_configure_mysql
* Adds function ubuntu1404_configure_apache: it is based on debian_configure_apache but the config files in /etc/apache2/sites-available are called 'invenio.conf' and 'invenio-ssl.conf' insthead of 'invenio' and 'invenio-ssl'

Tested on a fresh Ubuntu 14.04 installation