Added skip-link CSS classes to basic-HTML-version link.
Merge pull request #3187 from pjackson28/cleanupi18n

i18n: Removed a few unused i18n items
Optimised the skip link markup.
Merge pull request #3175 from thomasgohard/markup-skip-links

Optimised the skip link markup.
Merge pull request #3178 from thomasgohard/util-basic-html-version

Added skip-link CSS classes to basic-HTML-version link.
Lightbox: Added WAI-ARIA and support for aria-describedby and longdesc