Provide integration with UserVoice

Provide UI level integration with UserVoice. The back-end integration can be found at https://github.com/oaeproject/Hilary/pull/883.

When UserVoice is enabled, a `Feedback` link should be added to the footer. Depending on whether or not Terms and Conditions are enabled as well, this should look like this:

![screen shot 2014-05-02 at 10 19 52](https://cloud.githubusercontent.com/assets/109850/2861427/beea1a6a-d1de-11e3-8e50-55fcadcb7775.png)
![screen shot 2014-05-02 at 10 20 04](https://cloud.githubusercontent.com/assets/109850/2861428/bf051e82-d1de-11e3-90d7-93d610af6f5c.png)
![screen shot 2014-05-02 at 10 20 50](https://cloud.githubusercontent.com/assets/109850/2861429/bf05fd8e-d1de-11e3-9cf8-30a200abf786.png)