AU edition navigation changes

1. Comment to opinion
2. Media is replacing science position
3. Media should link to /au/media

![screen shot 2014-11-24 at 13 01 31](https://cloud.githubusercontent.com/assets/2579465/5165920/bb149b4e-73e2-11e4-9986-bda5692f0619.png)
![screen shot 2014-11-24 at 12 59 23](https://cloud.githubusercontent.com/assets/2579465/5165924/c5d9165e-73e2-11e4-82bc-488ec91813ab.png)