Make sysadmin dashboard gitlog date timezone-aware

@carsongee Just a small change to the sysadmin dashboard gitlog:
* Redundancy reduced in the template
* Date is timezone aware and formatted as `util.date_utils.DEFAULT_DATE_TIME_FORMAT`

Before:
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![before](http://i.imgur.com/71heogf.png)

After:
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![after](http://i.imgur.com/GnBQvzQ.png)