App status improvements

- switch to django naturaltime (better wording, fixes timezone issues)
- add "last sync" and split from "last submission"
- add color-based highlighting for last sync and submission
- also a bit of cleanup

![image](https://cloud.githubusercontent.com/assets/66555/3336377/9d1cb77a-f82c-11e3-904f-34d5c49cd84c.png)