Fix react warnings and part of backstage (#4706)

webapp/components/get_link_modal.jsx

@@ -90,10 +90,11 @@ export default class GetLinkModal extends React.Component {
                 className='form-control no-resize min-height'
                 ref='textarea'
                 value={this.props.link}
+                readOnly={true}
             />
         );
 
-        var copyLinkConfirm = null;
+        let copyLinkConfirm = null;
         if (this.state.copiedLink) {
             copyLinkConfirm = (
                 <p className='alert alert-success alert--confirm'>