Added custom attrib to expose network configuration thru Jig.
Added necessary relationships to support this.
Added NodeRef class to handle many to 1 relationship from Node to Network without modifying Node.
Added NodeObserver to clean up dangling NodeRefs and AllocatedIpAddresses on Node delete.
Updated unit tests to check cascading delete from Node to NodeRefs and AllocatedIpAddresses.
Merge pull request #171 from cdearborn/pull-req-master-2228b9de78b83874162b848d7e08af88fc2e1505

https://github.com/crowbar/barclamp-network/pull/171

Merged by devtool for VictorLowther