Changes made to HTML code to clear validation errors.

<file name>: <changes>
_title_bar: changed nav to div in order to use role="menu" and keep sub vie roles in place
_header: removed group tag (not needed) and " clear='all' " attribute from br tag (not allowed)
_document_list: changed aria-labeled-by to aria-label pr HTML5 validation
Merge pull request #23 from uclibs/feature/124_html5_validation

Changes made to HTML code to clear validation errors.