R1:410380be3f7a

Update Conpherence full message column UI

Summary:
Minor things

- Use radiused avatars like timeline
- Fix edge case with conpherence edited and date markers

Test Plan: Review a number of odd states in Conpherence full.

Reviewers: epriestley, btrahan

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12251