R1:ece651255c9e

Optimize mobile layout of DiffusionHistoryView

Summary: Little nits and spacing changes to viewing diffusion commit history on phones.

Test Plan:
Review in Chrome, iOS Simulator.

{F4990749}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18085