FEATURE: Update Font Awesome to v5.4.1 and SVGs (#6557)

* First take on subsetting svg icons

* FontAwesome 5 svg subset WIP

* Include icons from plugins/badges into svg sprite subset

* add svg icon support to themes

* Add spec for SvgSprite

* Misc. SVG icon fixes

* Use FA5 svgs in local-dates plugin

* CSS adjustments, fix SVG icons in group flair

* Use SVG icons in poll plugin

* Add SVG icons to /wizard

test/javascripts/widgets/widget-test.js.es6

@@ -217,7 +217,7 @@ widgetTest("handlebars d-icon", {
   },
 
   test(assert) {
-    assert.equal(this.$("i.fa.fa-arrow-down").length, 1);
+    assert.equal(this.$(".d-icon-arrow-down").length, 1);
   }
 });