Add time stamps to tag pages

Example month view:

![screen shot 2014-11-20 at 14 49 09](https://cloud.githubusercontent.com/assets/1001642/5126395/905615de-70c4-11e4-8fad-64e7e760e84e.png)

Example day view:

![screen shot 2014-11-20 at 14 49 22](https://cloud.githubusercontent.com/assets/1001642/5126401/954ddb1c-70c4-11e4-87f0-ee5517852fa4.png)