Accessibility standards require <th scope='row|col'> attributes (again, now for CKAN 2)

I first submitted this in pull request #124 (commit 50aad8db481e75d2a9d99d1cf86da99b6397ef2f against CKAN 1.7) which @amercader re-submitted in pull request #129, which was applied to release-v1.8, but it was never applied to the new templates in master.

This is a requirement for U.S. federal government websites (or at least ours), so it's a blocker for the HealthData.gov project.

Sorry about submitting this against release-v2.0 rather than against master. Keeping all of the branches straight is tricky...