add apache::package class for further use

This class is supposed to be used to install appropriate apache package
depending on parameters such as MPM. It also performs additional
OS-specific activities related to package installation. It's needed primarily
for FreeBSD, which will be supported after PR #264.
use ensure_resource to create apache user and group
Merge branch 'user' of github.com:mhellmic/puppetlabs-apache
Merge branch 'package_class' of github.com:ptomulik/puppetlabs-apache