[#1] Fix harvested datasets indexing

Reorder the setting of package_id and current on harvest_object so they
happen before the dataset creation
Add requirements to travis for dcat tests
Run the ckanext-sweden tests only
[#1] Fix deletions
[#1] Add harvesting tests

They require redis to be installed, as they will use the actual queues.
Also the harvest plugins need to be loaded and the --ckan option needs
to be used when running the tests.
[#1] Move dcat requirements to own folder
[#1] Update README with dcat harvesting instructions, and tests