Summary:
This is mostly in an effort to simplify D2323. Currently, we load one image into the database by default. This is a weird special case that makes things more complicated than necessary.
Instead, use a disk-based default avatar.
Test Plan: Verified that a user without an image appears with the default avatar as a handle, in profile settings, and on their person page.
Reviewers: btrahan, vrana, edward, jungejason
Reviewed By: vrana
CC: aran
Maniphest Tasks: T345
Differential Revision: https://secure.phabricator.com/D2331
