Make foreman integration optional

Instead of including foreman::params, the values are copied. That means 
foreman::params no longer needs to be included.

The next use of foreman is in puppet::server::config where it sets up 
reporting and ENC. This is wrapped in a new boolean $server_foreman. The user
will still need to take care of clearing $server_reports and
$server_external_nodes.

Fixes #154
I notice this logic is also in ```puppet::server``` so I wonder what's the best course of action here.