[#357] add link to event edit page in event show page

#357 活动页面可以跳转到修改页面 效果如下图：

![snip20130523_4](https://f.cloud.github.com/assets/1198651/552832/bf8a08ea-c36b-11e2-9b61-2ea7166db4a9.png)



![snip20130523_2](https://f.cloud.github.com/assets/1198651/552816/6ecb0b3e-c36b-11e2-9984-b3da59e842ea.png)



![snip20130523_5](https://f.cloud.github.com/assets/1198651/552834/c633e558-c36b-11e2-8c58-32b63d25b559.png)