Adds nestedColumns() function for calculating contextual columns widths

Alliteration!
Adds homepage image assets
Stubs out homepage news feed markup
Adds initial markup for homepage template and parts
Updates page-header piece to allow for CTA in title banner
Adds styling for right channel template variant on homepage
Adds styling for new page header with CTA button
Styles homepage news feed section

adds `.list-articles-home` module
Adds new image assets
Adds `.cta-short` extension of `.cta`

halves top & bottom padding on full-width cta block
Rewrites what was stitched-banner into something more flexible and sane
Adds some homepage-specific styling updates

Mostly to do with how the news feed articles are displayed across breakpoints
Adds background images to homepage 4-up grid section
Updates and extends `.cards` module for the homepage 4-up card block
Removes trailing backslash on $imagesFolder var

Was doubling up backslashes on me and 404-ing all my bg images...
Lightens the box shadow color on the homepage media feed image
Adds a new breakpoint to help with card shuffling across breakpoints.
Finalizes homepage markup
Updates homepage 4-up card markup

*  adds link to thumbnail image
*  adds excerpt missed on first pass
Adds microformatting classes for author meta on home news feed