Context for a specific url/item is now passed around via the metadata (metadata.set_context('key', 'val') and metadata.get_context('key', default='something')
The only other thing that was passed around in ArchivingContext was the storage info, which is already accessible now via self.config
* Removes (partly) the ArchivingOrchestrator
* Removes the cli_feeder module, and makes it the 'default', allowing you to pass URLs directly on the command line, without having to use the cumbersome --cli_feeder.urls. Just do auto-archiver https://my.url.com
* More unit tests
* Improved error handling
