Support Forward-Compatible CSS

[wesleyboar]

Goal

Add CSS processing plugin that supports forward-compatible CSS. Initially, just add support for these features:

• custom media queries

Background

1. CSS has features that are not yet supported by browsers.
2. Some of those features can be reliably polyfilled.
3. The PostCSS plugin postcss-preset-env compiles such polyfills to support many features.
4. @tacc-wbomar needs this features to reduce maintenance by having DRY code.

Requirements

1. PostCSS plugin postcss-preset-env must be added.
2. Feature custom-media-queries should be added.
3. Test for successful polyfill-ing must be available and documented.