records: exposing record metadata revisions

* Adds view tests for record revision API
  (addresses inveniosoftware/invenio#1990)

Signed-off-by: Bogdan Kulynych <bogdan.kulynych@gmail.com>
`url_for()` creates relative URL to the site root, while `test_web_page_content()` expects absolute URL, so I guess you'd need to do something like `test_web_page_content(CFG_SITE_URL + old_url, ...)` here.