Federated dt ux

Don't allow editing the destination tag if it was returned by a federation request.
Show the destination tag at the end of the address in the send form and the confirmation page.

Fixes #602.

A federated record that has a destination tag:
![screen shot 2014-08-08 at 2 15 35 pm](https://cloud.githubusercontent.com/assets/3108007/3862948/b34613a2-1f41-11e4-9607-2f9bd1ae9cbc.png)

The confirmation page:
![screen shot 2014-08-08 at 2 16 14 pm](https://cloud.githubusercontent.com/assets/3108007/3862975/2569ce06-1f42-11e4-864d-959925bb1f1a.png)

Federated results that require a destination tag still work as expected:
![screen shot 2014-08-08 at 2 17 09 pm](https://cloud.githubusercontent.com/assets/3108007/3862989/387fdcf6-1f42-11e4-95e4-894c91d031a1.png)