Rolls color exports into custom POSTCSS lib

[drolsen]

Replaces our colors-export gulp task(s) with custom postcss plugin.

This does a few things for us:

• Removes the need for more plugin dependencies.
• Control over our colors JSON formatting.
• Removes extra watch task around exported JSON file that previously prevented build loop.

Description

• Adds new 'styleguide' path helper
• Adds new POSTCSS export-colors lib
• Adds export-colors lib to postcss-plugins stream
• Removes color export/watch from gulp.js file
• Renames SgColorSwatch__variables.json to SgColorsSwatch__Colors.json
• Removes gulp-task required plugins from package.json

Motivation and Context

The motivation behind this is to remove duplicate watch process on top of webpack-dev-server and inherit the colors export into the dev workflow.

How Has This Been Tested?

• run npm or yarn dev.
• open colors page.
• edit a colors name in source/elements/variables/colors.css, see change in colors page.
• edit a colors value in source/elements/variables/colors.css, see change in colors page.
• confirm npm or yarn build, production and watch all still work

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[bstaruk]

This is awesome! I wish I had thought of this myself :)

I do have a couple notes though:

• name at colors-export.js:7 could be defined via const (prefer-const)
• jsonObject at colors-export.js:43 could be defined via const (prefer-const)
• missing EOL semicolon at colors-export.js:72 (semi)

These are just code style tweaks that'll bring the file inline with our eslint presets/rules.

I'd be happy to make these changes myself, just give me the word. Wanted to make sure you were aware before I made any moves.