base: various HTML5 fixes

* [`link`](http://www.w3.org/TR/html5/document-metadata.html#the-link-element) are empty tags and do not require a closing tag.
* specifying a `role=navigation` to a `nav` is redundant is [not recommended](http://www.w3.org/TR/html5/dom.html#aria-usage-note).
* `rev` is obsolete.
* `meta Content-Type` is redundant.
* `meta Content-Language` is obsolete.

How to reproduce:
* http://validator.w3.org/check?uri=http%3A%2F%2Finvenio-demo-next.cern.ch%2F&charset=%28detect+automatically%29&doctype=Inline&group=0