More complete node summary

[paulbellamy]

Base work for #1105 and #1159

Could use more refactoring eventually, as the RenderableNode json rendering is never really used after this. We either render the NodeSummary or the detailed.Node. Might also be worth splitting detailed and summary into different packages, but that will conflict with changes in #1126.

With this change the topology views (and deltas) include the nodes' metadata and metrics (sans samples). e.g.

{ nodes: [
  process:scope:1716: {
    id: "process:scope:1716",
    label: "/home/weave/weaver",
    label_minor: "scope (weave:1716)",
    rank: "/home/weave/weaver",
    shape: "square",
    linkable: true,
    metadata: [
      {
        id: "threads",
        label: "# Threads",
        value: "12",
        prime: true
      },
      ...
    ],
    metrics: [
      {
        id: "process_memory_usage_bytes",
        label: "Memory",
        format: "filesize",
        value: 46587904,
        samples: [ ],
        min: 0,
        max: 46587904,
        first: "2016-03-15T12:00:58.106201326Z",
        last: "2016-03-15T12:01:12.065987896Z"
      },
      ...
    ]
  }
]}

@tomwilkie, wdyt?

[tomwilkie]

Superceeded by #1204