Create quads hierarchy

* Move nquads into quad.
* Create cquads simplified parser in quad.
* Move Triple (renamed Quad) to quad.

Also made sure mongo actually implements BulkLoader.
Temporarily use cquads only

I intend to make this configurable, but there is tight connection
between db.Load and db.Open that is getting in the way of that.

Testing on data set 30kmoviedata.cq.gz created by doing:

zcat 30kmoviedata.nq.gz | sed 's/[<>]//g' | gzip -c > 30kmoviedata.cq.gz

The following query is successful:

[{
  "type": "/film/film",
  "name": null,
  "/film/film/directed_by": {
    "name": "David Fincher"
  },
  "/film/film/starring": [{
    "/film/performance/actor": {
      "name": null
    }
  }]
}]

TODO: fix up naming for quads and make strict parsing an option.