support multiple datasets, uploading non-tabulr resources, dump log

[OriHoch]

This PR contains several changes which I needed for ckanext-upload_via_email:

• Support loading multiple datasets, providing the dataset properties dynamically.
• Support for uploading non-tabular resources to CKAN (not just storing the URL)
• Output a resource with log of created datasets/resources or error details

Also some minor changes:

• Support setting the ckan host via env var
• Support for setting resource name with special chars
• Allow to extend the add_ckan_resource processor

I tried to keep backwards compatibility so existing pipelines shouldn't be affected by the changes

See updated docs and test for usage details.

[roll]

@akariv
@OriHoch
We need someone else (not Brook) to review it..