[shared file view] rewrote with react (#3191)

* rewrote 'file view' with react for audio, document, spreadsheet, svg,
unknown files
* code improvement for 'video' file
* bugfix

frontend/src/shared-file-view-unknown.js

@@ -0,0 +1,25 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+import SharedFileView from './components/shared-file-view/shared-file-view';
+import SharedFileViewTip from './components/shared-file-view/shared-file-view-tip';
+
+const { err } = window.shared.pageOptions;
+
+class SharedFileViewImage extends React.Component {
+  render() {
+    return <SharedFileView content={<FileContent />} />;
+  }
+}
+
+class FileContent extends React.Component {
+  render() {
+    if (err) {
+      return <SharedFileViewTip />;
+    }
+  }
+}
+
+ReactDOM.render(
+  <SharedFileViewImage />,
+  document.getElementById('wrapper')
+);