replace tree with index content (#2819)

frontend/src/components/index-viewer.js

@@ -0,0 +1,33 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import MarkdownViewer from '@seafile/seafile-editor/dist/viewer/markdown-viewer';
+
+const viewerPropTypes = {
+  onLinkClick: PropTypes.func,
+  onContentRendered: PropTypes.func.isRequired,
+  indexContent: PropTypes.string,
+};
+
+class IndexContentViewer extends React.Component {
+
+  onLinkClick = (event) => {
+    event.preventDefault();
+    this.props.onLinkClick(event);
+  }
+
+  render() {
+    return (
+      <div className="markdown-content">
+        <MarkdownViewer
+          markdownContent={this.props.indexContent}
+          onContentRendered={this.props.onContentRendered}
+        />
+      </div>
+    );
+  }
+
+}
+
+IndexContentViewer.propTypes = viewerPropTypes;
+
+export default IndexContentViewer;