Add queue indirection as an option for catalog storage.

This eventually will allow catalog storage ("storeconfigs") to be taken out of the critical request-handling path of puppetmasterd, such that:

• Puppet::Node::Catalog can be serialized to a message queue via the indirector's "save" method
• a separate process can use Puppet::Node::Catalog::Queue.subscribe to pick up these catalog objects as they come in and can save them to the database through the :active_record terminus