Normalize "within" properties

[stephenwf]

When resource come in, they may have a "within" property. That property might related to a layer, collection or manifests inside of the resource, or an external resource. This should be calculated and normalized from:

{
    "within": "http://collection.json"
}

to:

{
    "within": {
        "@id": "http://collection.json",
        "@type": "sc:Collection"
     }
}

If it is known what type of resource it is use that, or else assume its an external resource. When an external resource is loaded, we can pro-actively go back and update its definition.