posts by registered users with no first/last name now display their usernames, non-registered ones display Anonymous

Summary: Now posts by registered users with no real names display their usernames and for non-registered ones displays Anonymous

Test Plan: Post by a registered user with no real names http://grab.by/xdsq, Post by an anonymous user http://grab.by/xdss, post by a user with names

Reviewers: rjmackay, shadowhand

Reviewed By: rjmackay, shadowhand

Subscribers: dkobia, srutto, eyedol, rjmackay

Maniphest Tasks: T162

Differential Revision: https://phabricator.ushahidi.com/D132