Add class causing expading on full width on mobile

[crishpeen]

Override containers padding to expand on full width on mobile. Something like:

@media (max-width: @screen-xs-max) {
    .expand-xs {
        margin-left: floor(-(@grid-gutter-width / 2));
        margin-right: ceil(-(@grid-gutter-width / 2));
    }
}

[adamkudrna]

Inspiration for a complex solution: https://css-tricks.com/full-width-containers-limited-width-parents