Refactor and document colour variables
Merge branch 'styleguide' of https://github.com/guardian/mobile-apps-article-templates into styleguide

Conflicts:
	ArticleTemplates/assets/css/style.css
	ArticleTemplates/assets/scss/layout/_article--audio.scss
	ArticleTemplates/assets/scss/layout/_article--liveblog.scss
	ArticleTemplates/assets/scss/layout/_discussion.scss
	ArticleTemplates/assets/scss/layout/_football.scss
	ArticleTemplates/assets/scss/layout/_support.scss
	ArticleTemplates/assets/scss/modules/_aside.scss
	ArticleTemplates/assets/scss/modules/_figure.scss
	ArticleTemplates/assets/scss/modules/_tabs.scss
	ArticleTemplates/assets/scss/modules/_tags.scss
	ArticleTemplates/assets/scss/modules/blocks/_comment.scss
	ArticleTemplates/assets/scss/modules/charts/_bar-chart.scss
	ArticleTemplates/assets/scss/modules/containers/_card.scss
	ArticleTemplates/assets/scss/modules/containers/_container.scss
	ArticleTemplates/assets/scss/modules/content/_meta.scss
	ArticleTemplates/assets/scss/modules/content/_prose.scss
	ArticleTemplates/assets/scss/modules/football/_football-fixture.scss
	ArticleTemplates/assets/scss/modules/football/_match-summary.scss
	ArticleTemplates/assets/scss/modules/football/_player-card.scss
	ArticleTemplates/assets/scss/modules/media/_audio-player.scss
	ArticleTemplates/assets/scss/modules/witness/_contribute.scss
	ArticleTemplates/assets/scss/modules/witness/_embed.scss