UPDATE: Adds web app (#79)

Things missing:

* Browse mode
* Front end tests
* Storybook

webapp/src/App.tsx

@@ -0,0 +1,59 @@
+import "./App.css";
+import Workbook from "./components/workbook";
+import "./i18n";
+import styled from "@emotion/styled";
+import init, { Model } from "@ironcalc/wasm";
+import { useEffect, useState } from "react";
+import { WorkbookState } from "./components/workbookState";
+
+function App() {
+  const [model, setModel] = useState<Model | null>(null);
+  const [workbookState, setWorkbookState] = useState<WorkbookState | null>(
+    null,
+  );
+  useEffect(() => {
+    async function start() {
+      await init();
+      const queryString = window.location.search;
+      const urlParams = new URLSearchParams(queryString);
+      const modelName = urlParams.get("model");
+      // If there is a model name ?model=example.ic we try to load it
+      // if there is not, or the loading failed we load an empty model
+      if (modelName) {
+        try {
+          const model_bytes = new Uint8Array(
+            await (await fetch(`./${modelName}`)).arrayBuffer(),
+          );
+          const _model = Model.from_bytes(model_bytes);
+          if (!model) setModel(_model);
+        } catch (e) {
+          const _model = new Model("en", "UTC");
+          if (!model) setModel(_model);
+        }
+      } else {
+        const _model = new Model("en", "UTC");
+        if (!model) setModel(_model);
+      }
+      if (!workbookState) setWorkbookState(new WorkbookState());
+    }
+    start();
+  }, [model, workbookState]);
+
+  if (!model || !workbookState) {
+    return <Loading>Loading</Loading>;
+  }
+
+  // We could use context for model, but the problem is that it should initialized to null.
+  // Passing the property down makes sure it is always defined.
+  return <Workbook model={model} workbookState={workbookState} />;
+}
+
+const Loading = styled("div")`
+  height: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-size: 36px;
+`;
+
+export default App;