Make Pholio mock image thumbnails publicly visible

Summary:
Refs T2652 - This should make all of Pholio mocks publicly visible

The rest that is to be done is more generic, like the ActionListView etc.

Test Plan: set mock to public, visited it in another browser without user session

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2652

Differential Revision: https://secure.phabricator.com/D5454