Give application actors in feed reasonable icons
Ref T8952. Currently, when an application (most commonly Herald, but sometimes Drydock, Diffusion, etc) publishes a feed story, we get an empty grey box for it in feed.
Instead, give the story a little application icon kind of "profile picture"-like thing.
Here's how it looks:
Feel free to tweak/counter-diff.
Reviewed By: chad
Maniphest Tasks: T8952
Differential Revision: https://secure.phabricator.com/D15773