Show invitee username

![screenshot from 2014-12-10 14 36 39](https://cloud.githubusercontent.com/assets/464938/5376715/fcfbe8a2-8079-11e4-8123-47a75219c440.png)
Merge PR in ix first: stellar/ix#424
Closes: #1005
Made it a little wider because it now contains username too.