Add height-fit helper similar to width-fit

[kevinsawicki]

For things on mobile, it can be helpful to cap the max-height of certain elements at 100% so the element does not overflow the page.

For example, height-fit would be useful for a box overlay of indeterminate height that you don't want to overflow the bottom of the viewport but instead want the inside of the box to scroll.

[jonrohan]

Included in 10.4.0