Refactor columns.sass to use map values

[james-wasson]

This is an improvement.

This is an improvement in readability to the columns.sass.

There are too many blocks of code repeating .is-one-third-* over and over.

Proposed solution

We are using a name-value map to reference very well defined variable-name values and looping through them rather than specifying each one directly.

Note: Decreased the file size by more than half (~300 lines)

Tradeoffs

This solution may increase build time - but not substantially.

Testing Done

These changes do not affect the output CSS file

I did look at the documentation site to ensure all changes are working correctly

Changelog updated?

Yes.