fetch username for inflation dest, if needed

I verified at a quick glance in services/contacts that the
fetchContactByAddress method will only make a request if the contact
isn't already stored in localStorage.
only fetch inflation destination if present

surprise: if you hit refresh on the settings page, for some reason the
inflation destination isn't ever valid. Let's not make our federation
request in that case.
Merge pull request #1004 from jakswa/js/infl-dest-fed

fetch username for inflation dest