-enabled to cancel(remove) messages that are sent just before

## Overview

Added the function to cancel(remove) messages that are sent just before.

## Explanation

### Sent notification and canceled message notification

The color of mark is **GREEN** means **Success**.

![atmosphere-sent-and-cancelled](https://f.cloud.github.com/assets/2914192/1632501/efa9f6d8-5778-11e3-89d0-9e0432ef0e91.png)

### Error notification

The color of mark is **RED** means **Error**.

![atmosphere-send-failed](https://f.cloud.github.com/assets/2914192/1632510/fd7480bc-5778-11e3-9c77-e63f56b00399.png)

## Remarks

The library to show notification was changed from [jGrowl](http://plugins.jquery.com/jgrowl/) into [Messenger](https://github.com/HubSpot/messenger), so the design of notification was also changed.