Add Provenance information to addresses

Provenance now looks like this:

```
{
  "activity" => {
    "executed_at"=>2014-01-01 00:00:00 UTC,
    "processing_scripts"=>"https://github.com/OpenAddressesUK/distiller",
    "derived_from"=>[
      {
        "type"=>"Source",
        "urls"=>[
          "http://ernest.openaddressesuk.org/addresses/1"
        ],
        "downloaded_at"=>2014-01-01 00:00:00 UTC,
        "processing_script"=>"https://github.com/OpenAddressesUK/distiller/tree/sdasdasdasd/lib/distil.rb"
      },
      {
        "type"=>"Source",
        "urls"=>[
          "http://alpha.openaddressesuk.org/postcodes/kHPXpu"
        ],
        "downloaded_at"=>2014-01-01 00:00:00 UTC,
        "processing_script"=>"https://github.com/OpenAddressesUK/distiller/tree/sdasdasdasd/lib/distil.rb"
      },
      {
        "type"=>"Source",
        "urls"=>[
          "http://alpha.openaddressesuk.org/streets/WSahdR"
        ],
        "downloaded_at"=>2014-01-01 00:00:00 UTC,
        "processing_script"=>"https://github.com/OpenAddressesUK/distiller/tree/sdasdasdasd/lib/distil.rb"
      },
      {
        "type"=>"Source",
        "urls"=>[
          "http://alpha.openaddressesuk.org/towns/iyttWM"
        ],
        "downloaded_at"=>2014-01-01 00:00:00 UTC,
        "processing_script"=>"https://github.com/OpenAddressesUK/distiller/tree/sdasdasdasd/lib/distil.rb"
      }
    ]
  }
}
```