Use semantic elements where possible, simplify html structure, improve screenreader experience

Ensure that the article title is the sole h1

• (or at least the first h1, in cases where multiple h1s are created by authors of the wiki page)

• this change allows people using screenreaders to quickly discern what the page is about, without affecting visual hierarchy.

Flatten 'body-container' to body element

• div.body-container appears(?) unnecessary, as the parent body element could serve the same role.

• less nesting makes it easier to debug html + css :)

Replace divs with semantic elements

• improves screenreader experience

• makes css debugging easier!