new: usr: add timer for the acceptance of the challenge #4

assets/js/mine-seeker/components/index.js

@@ -10,6 +10,7 @@
 export { GameBoard } from './GameBoard';
 export { default as OnlinePlayersDialog } from './OnlinePlayersDialog';
 export { default as WaitingOverlayContent } from './WaitingOverlayContent';
+export { default as ChallengeCountdown } from './ChallengeCountdown';
 export { default as GameTimer } from './GameTimer';
 export { default as GridControl } from './grid/GridControl';
 export { default as GridField } from './grid/GridField';