docs(guide/accessibility): Content updates

Also includes new section on ngMessages
docs(ngAria): Add Usage Details and Examples

Closes #10031
docs(nav): highlight current nav-index-listing

Color the current nav-index-listing item dark red
to make it easier to know where you are.

Closes #9970
Closes #9974
fix($http): don't parse single space responses as JSON

Closes #9907
feat($location): allow to location to be changed during $locationChangeStart

Closes #9607
Closes #9678