Replace 'author', 'owner' etc. actors with new 'agent' extra field.

Initial replacement: start from api tests, just insert values to db, no actual validation.
Fix rest of tests with new agent field
Use a normal user for many tests instead of a sysadmin
Define agent roles in settings
Test that required fields exist in data_dict and refactor api tests a bit
Update UI to use agents, needs a bit of fixing still
Prevent error in agent getters
Fix funder and owner in form
Fix errors from agent getters
Agent handling with UI
Fix Selenium tests
Comment out all things related to 'projdis' field
Some sketch for testing RDF export in test_api.py
Validate agents for compulsory fields
Fix funder, owner validation. Fix author role preserving when adding authors.
Add TODO for some exception.
Fix funder, owner validation. Fix showing agents of a dataset.
Merge branch '507-more-agents-improvement' into development

Conflicts:
	ckanext/kata/controllers.py
	ckanext/kata/plugin.py
	ckanext/kata/tests/functional/test_api.py
	ckanext/kata/theme/templates/package/snippets/package_basic_fields.html
	ckanext/kata/validators.py