Support mapping array values (lens)

[JaceHensley]

I'm not quite sure how this would look but the idea is to allow displaying an array of mapped items. For example if you have the following JSON:

{
  "things": [
    {
      "value": "first"
    },
    {
      "value": "second"
    }
  ]
}

you may want the wallet to display:

Value of Things: first, second

[brentzundel]

closing as subset of #4