Tables/figures should be full width (at least on small screens)

[davidfarmer]

From Jiri Lebl

In the HTML output, currently tables and figures have an unnecessary border around
them which is fine on large screens but an issue on small screens. The border should
be taken off on small screens. Probably centering tables and having no border should
be the right thing always not just on small screens, when scrolling is necessary,
the table I feel should just go all the way to the edge of the screen.