(Facets) Facet searches on resource type

There is now a `facets` object on the search results. Example result:

```json
{
  "total": 1,
  "results": [
    {
      "resourceType": "user",
      "id": "u:cam:VVR0wpRSxM",
      "tenantAlias": "cam",
      "displayName": "Branden Visser",
      "visibility": "public",
      "profilePath": "/user/u:cam:VVR0wpRSxM",
      "thumbnailUrl": "/api/download/signed?uri=remote:https://si0.twimg.com/profile_images/987425409/me1_normal.jpg&signature=eec7c2d39276c133a19d59b5cfc7e75a7c20631c&expires=1368090000000",
      "tenant": {
        "alias": "cam",
        "displayName": "Cambridge"
      }
    }
  ],
  "facets": {
    "resourceTypes": {
      "total": 1,
      "items": [
        {
          "term": "user",
          "count": 1
        }
      ]
    }
  }
}
```

`resourceTypes` is a "name" of many different types of facets we can have (resourceTypes is a "term" facet that facets on the "resourceType" field).

`total` is the total number of unique facets that were matched (it is possible to page the facets themselves, I believe)

`items` is a list of the facets in the current facet-page

Then each item has a "term", for the value that matched the facet term, and a "count", which is how many total items in the search index would match the query with that facet value.