Add demo (#2502)

* Add demo

* Fix stuff

* Lint

* Typescript and demo card

* More fixes

* Allow switching through configs

* Lint

* Lint2

* Add two demo configs

* Lint

* Lint

demo/src/entrypoint.ts

@@ -0,0 +1,19 @@
+import "@polymer/paper-styles/typography";
+import "@polymer/polymer/lib/elements/dom-if";
+import "@polymer/polymer/lib/elements/dom-repeat";
+
+import "../../src/resources/hass-icons";
+import "../../src/resources/ha-style";
+import "../../src/resources/roboto";
+import "../../src/components/ha-iconset-svg";
+
+import "./ha-demo";
+
+/* polyfill for paper-dropdown */
+setTimeout(
+  () =>
+    import(/* webpackChunkName: "polyfill-web-animations-next" */ "web-animations-js/web-animations-next-lite.min"),
+  1000
+);
+
+document.body.appendChild(document.createElement("ha-demo"));