[#16] Handle organizations on API requests

After the latest changes in the EC API, the API endpoints for requesting
the creation of a dataset and a file are the following:

* /Datasets/Organisation/2
* /Files/Organisation/2/Dataset/3

Several changes were required to support this:

* Update logic to get the relevant endpoints
* Update logic to handle separate endpoints for read / write
* Update mock EC API with new endpoints
* Update CKAN auth settings to force all datasets to belong to an org
* Update actions to get the relevant EC API ids when performing a
  request
* Update tests
Add current custom config options to README
[#20] Add role for ckanext-harvest
Merge branch 'master' into 45-ec-harvester