Update job keys changed on 9ba6e8f
[#5] Add helper function for generating a link to a harvest object
[#5] Add method for returning the original URL for a document

Harvesters implementing IHarvester can define a `get_original_url`
method that should return a URL pointing to the original location of a
document in the remote server. If present, this URL will be used on the
job reports.

Examples:
* For a CKAN record: http://{ckan-instance}/api/rest/{guid}
* For a WAF record: http://{waf-root}/{file-name}
* For a CSW record: http://{csw-server}/?Request=GetElementById&Id={guid}&...
Document  method and cleanup the interface file