改进销售统计

#### 1. 修正总金额显示为 `0.3300000000000001` 的问题

![screen shot 2013-09-09 at 9 07 47](https://f.cloud.github.com/assets/15178/1106874/1c97e8dc-1951-11e3-9b2d-04de45871c19.png)

#### 2. 统计面板改得霸气一点

![screen shot 2013-09-09 at 9 09 12](https://f.cloud.github.com/assets/15178/1106871/1600c322-1951-11e3-880a-a8bfc5731714.png)

https://github.com/19wu/19wu/pull/566