Dgeni is now providing the `id` for all the documents to be viewed. So we
no longer need to add this to the DocumentContents object.
There are some notable changes in the refactoring:
`DocumentService`:
* The id of the document to render is now obtained from `LocationService.path()`.
* The `getFileNotFoundDoc` and `getErrorDoc` methods have been extracted from
the `fetchDocument` method.
`AppComponent`:
* the `pageId` is now computed in a separate `setPageId` method.
`AppComponen` spec file:
* The `TestHttp` has had the hard coded documents removed and replaced with
a function that will generate docs as needed.
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