[229] Adds a last_major_modification extra to the package

When a resource is added, or deleted the last_major_modification is updated to today's date.
If the URL of an existing resource is modified, the same change is made.

Unfortunately CKAN uses the same function name in two different plugins which means that
they can't both be in a single plugin :( meaning we've added two new plugins which will
require a re-setup.py

Display the last_major_modified instead of metadata modified

Added a one-off migration and modified templates
[229] Fix for updated value due to dict/obj confusion
[522] Make sure users are sent with the edited publisher
[229] A non-pretty fix to show new extra on the search results page.

When editing a dataset the normal workflow happens and ends up with the package
represented as a dict, and then the resource plugins that we use to are given
instances of the sqlalchemy models making it impossible to add extra within these
plugins. Rather we can add the extras, but we can't add them to the package dict
that is about to be indexed.

This is probably only an issue if we want to add fields to the package/package extras
within the resource plugins.
[229] Remove explicit last_major_modification from the schema
Merge commit '49182a8b' into stable

Conflicts:
	ckanext/dgu/forms/dataset_form.py
	ckanext/dgu/plugin.py
[229] "Last updated" improvement - Major sort out, with tests now passing. Appears to work, displaying the new modification date, sorting by it in the search results and bin/initial_last_major_modification.py sets the existing values. Install at end of day, restart SOLR, add the new dgu_package_updates plugin, run script overnight.

Conflicts:

	ckanext/dgu/lib/helpers.py
	ckanext/dgu/tests/test_resource_changes.py
	test-core.ini
[229] "Last updated" improvement - typo.
[229] "Last updated" improvement - Feed and home-page APIs now used last_major_modification. Fixed display of "Created" in search result. Renamed plugins to show the purpose better. Merged plugins.

Conflicts:

	ckanext/dgu/controllers/api.py
	ckanext/dgu/plugin.py
	setup.py
[229] "Last updated" improvement - Fix merge for weird whitespace issue.