Combine separate efforts for grid mixins into one, cleanup and reorganize
restore var to customizer
Merge branch 'master' into restore_grid_mixins

Conflicts:
	dist/css/bootstrap.min.css
Merge branch 'master' into restore_grid_mixins

Conflicts:
	dist/css/bootstrap.min.css
Merge pull request #11050 from twbs/restore_grid_mixins

Restore grid mixins