Update landmark rules per ARIA 1.3

[shunguoy]

WAI-ARIA 1.3 added sectionfooter and sectionheader to handle how nested headers and footers are handled.

• The sectionheader: Maps directly to a element that is a descendant of sectioning content.
• The sectionfooter: Maps directly to a element that is a descendant of sectioning content

The affected rules: All landmark rules could be potentially affected when they need to calculate unique labels, specifically, the following two rules need to be re-worked:

• aria_contentinfo_single and aria_barnner_single