Add All channels link to dashboard template

Please add a channels link in the left nav. This should be styled the same as the "All campaigns" link See screenshot:
![screen shot 2013-07-17 at 4 36 57 pm](https://f.cloud.github.com/assets/1521387/812712/8acb1608-eef4-11e2-97ef-f926f2a8efcb.png)

Please add the 'body' of the current channels page: http://qa-vumi.za.prk-host.net/channels/  to the 'body' of the dashboard page. This view is displayed when a user clicks "All channels" in the left nav. In other words, instead of having a separate channels page, we display the channels in the dashboard template when a user clicks "All channels" See screenshot: 
![screen shot 2013-07-17 at 5 21 12 pm](https://f.cloud.github.com/assets/1521387/812730/b6cfc924-eef4-11e2-8f63-71e7dc4d8087.png)