R1:ae27ce0f7d91

Tweak mobile timeline

Summary: Improves timeline legebility by pulling date inline with title in timeline mobile.

Test Plan: shrink screen for a task, see new layout

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D7236