Tweak DCAT markup

I've tweaked the DCAT markup so the download page is a `dcat:Catalog`, and each type (with and without provenance) is a `dcat:Dataset` with two `dcat:distribution`s - one for JSON and one for CSV.

I've also changed the `dct:format` to be the actual file format, rather than zip, and added a `dct:type` of `:indirect-access` to reflect the fact that access to the data is not direct (as outlined in http://www.w3.org/2011/gld/wiki/Data_Catalog_Vocabulary/Recipes#How_to_describe_a_distribution_based_on_a_CSV_compressed_into_a_ZIP_file). 

Finally, I've added the torrent files to the /public directory, as they're so small it probably doesn't make much sense putting them in S3. These will need to be changed once @pikesley has updated the URIs.