Edit the secret key during registration

Allow editing the secret key during registration.

Fixes #99.

![screen shot 2014-10-27 at 7 54 41 pm](https://cloud.githubusercontent.com/assets/3108007/4802915/f3464bde-5e4d-11e4-806a-a5f7fe834eea.png)

![screen shot 2014-10-27 at 7 54 59 pm](https://cloud.githubusercontent.com/assets/3108007/4802914/f3455b16-5e4d-11e4-9552-4543a51c2d89.png)