Implement Clock widget

This implements a clock widget that update every time a `sync` message occurs.

![index](https://cloud.githubusercontent.com/assets/198739/3293024/44a54442-f596-11e3-83e5-aa44ad161c2e.png)
![index2](https://cloud.githubusercontent.com/assets/198739/3293025/467c85d2-f596-11e3-81c4-778aec13fbb4.png)