Include Sass function and support inline SVGs as background images

Problem/Motivation

For even greater flexibility, we could also compile a Sass map with inline SVG data for use in the background-image property. As noted in this post, data URLs have several advantages. One limitation is that the color(s) of the icon cannot be changed using "fill" or "stroke" properties; ideally a solution here would be to allow for token replacement with a Sass function when defining an icon class.

Proposed resolution

In addition to creating SVG sprites, we will also create an SCSS file with a Sass map of all SVG data. Additionally, following the method described here, we will append a Sass function for retrieving a particular icon and colorizing it as needed. Themes will then just need to import the map and create icon classes as needed.