The new breakpiont-limited class pattern is to omit the breakpoint size when using the lowest size eg. col-xs-12 to col-12. This commit implements this pattern to the grid system.
* Fixes#20775 without adding extra width and an important flag
* Since we're now getting the extend, we don't need the extra position relative
* rerrange
* getting min-height from the extend already
- Restores two-mixin approach to generating semantic grid columns (now with 'make-col-ready' and 'make-col')
- Removes need for .col-xs-12 by restoring the mass list of all grid tier classes to set position, min-height, and padding
- Adds an initial 'width: 100%' to flexbox grid column prep (later overridden by the column sizing in 'flex' shorthand or 'width') to prevent flexbox columns from collapsing in lower viewports
- Flexbox responsive behavior fixed with specific .col-{breakpoint} classes now added
- Dropped the make-col mixin in favor of a column-basics placeholder that we can extend across our grid infrastructure
- Updated docs to use required .col-xs-12 (as a safeguard for when folks enable flexbox mode--this isn't necessary in default grid mode)
- Update flexbox grid docs to include responsive docs, tweak some other bits too
A more idiomatic refactoring of the grid framework
* Use %-placeholder instead of generating a class name list
* Use if expression
* Remove loop-grid-columns
