Stop propagation of click events on the background

This is to prevent the bubbled-up clicks from triggering changes behind the modal overlay (e.g., the auto-closing of open dropdowns).
Access correct data attribute for reveal settings
Merge pull request #4461 from metalspawn/fix-multi-window-reveal-with-ajax

Access correct data attribute for reveal settings
Merge pull request #4444 from gaborluk/patch-1

Stop propagation of click events on the background
Add metadata to SCSS files
Added important to the centered column mixin to avoid specificity issues
Hide the background in reveal initially to resolve an issue if CSS loads slowly
Merge branch 'master' into 5-flexbox

Conflicts:
	scss/foundation/components/_grid.scss