improve gateway rendering
improve gateway rendering

* follow through gateways when determining whether a node is connected to
  a node in a group

* only show gateways if both ends are connected to nodes in groups being
  shown

pivotal-devin-fallak/atc,zachgersh/atc,pivotal-devin-fallak/atc,savaki/atc,utako/atc,savaki/atc,zachgersh/atc,simonjjones/atc,utako/atc,savaki/atc,zachgersh/atc,utako/atc,simonjjones/atc,pivotal-devin-fallak/atc,zachgersh/atc,simonjjones/atc