Rename ConfirmPageContainerHeader class (#7322)

The class has been renamed to reflect that it is a header, to avoid
having the same name as the `ConfirmPageContainer` component. Multiple
components with the same name can lead to confusing error messages.

ui/app/components/app/confirm-page-container/confirm-page-container-header/confirm-page-container-header.component.js

@@ -6,7 +6,7 @@ import {
 } from '../../../../../../app/scripts/lib/enums'
 import NetworkDisplay from '../../network-display'
 
-export default class ConfirmPageContainer extends Component {
+export default class ConfirmPageContainerHeader extends Component {
   static contextTypes = {
     t: PropTypes.func,
   }