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
This is the reason we should usually not override tag style (especially changing a span to a block).
The spans just inside ```div.invite-row``` should really be divs with a class like ```.invite-item``` that floats left.