Questionnaire transfers

This allows users to transfer a dataset to another user.

This is currently deployed to staging (though you have to remember to edit the urls in the mails from 'certificates.theodi.org' to 'staging.certificates.theodi.org')

You now get an "edit settings" option next to a dataset title:

![screen shot 2013-09-30 at 16 43 10](https://f.cloud.github.com/assets/51385/1238299/0effc81a-29e7-11e3-8f7c-bcff8fec1e24.png)

which opens this dialog:

![screen shot 2013-09-30 at 16 44 05](https://f.cloud.github.com/assets/51385/1238306/302ee6a6-29e7-11e3-9f9c-a9c7bba71971.png)

the link updates to give the option to cancel:

![screen shot 2013-09-30 at 16 33 31](https://f.cloud.github.com/assets/51385/1238313/464823b2-29e7-11e3-8203-355ff4f57f17.png)

---

the other user can visit the link and get the option to claim the dataset:

![screen shot 2013-09-30 at 16 36 07](https://f.cloud.github.com/assets/51385/1238328/77a35792-29e7-11e3-8aed-0b9d46405fa5.png)

### todo

- [ ] localise text

Resolves #585