Update sections where WCAG2ICT says Level AAA is not addressed in the document

[maryjom]

There are a few sections that have content saying that Level AAA SC are not in the document. These statements will have to be modified to provide the correct information and context regarding Level AAA SCs. The sections are:

• Background
• Interpretation of Web Terminology in a Non-web Context - last paragraph
• Glossary Items Used Only in AAA Success Criteria
• May need to add something to the SOTD once AAA start getting addressed
• Need to keep the Comparison with the 2013 WCAG2ICT Note updated with AAA SCs added (or add a new section with the changes in this version...)