Changes the approach for the grid classes from this:
<div class="col-sm-9 col-push-sm-9"></div>to something a bit more succinct:
<div class="col col-sm-9 push-sm-9"></div>The motivation for this was primarily to shorten class names if we went with fractional classes (e.g., .col-sm-1-3) so we don't end up with something like .col-push-sm-1-3 and the like. Haven't leaned into the fractional stuff yet though to explore that.
/cc @twbs/sass