Stop page extending out of viewport width by 40px

Currently the .container and .wrapper-footer elements are set to 100%, and also have horizontal padding added to them. This results in a total width of greater than the full width of the viewport; This causing the
browser to scroll horizonally into empty space, regardless of how wide the viewport is.

I had added the `box-sizing: border-box` to these elements in order to resolve this.

Cheers,
Louis

P.S. I've emailed my contributor agreement to Jennifer. :paperclip: