Footnotes: Increased width+spacing of links in SCSS. Fixes gh-5448.

@nschonni Is there some kind of pre-existing naming scheme in place? Should it be good with slapping on "footnotes-" to the beginning of its variables?

IIRC, in WET 3.1 there's a naming scheme (or at least an implied one :P) for placeholder selectors, but I'm not sure where things stand in WET 4.x and how variables are expected to be treated.