Align table cell content in Diffusion.
Summary: Most cells in Diffusion were aligning text to the top, and the sigil height is fixed. This lines all up on center.
Test Plan: Tested diffusion with new cell alignment, clicked around to other tables. Looks good in Chrome.
Reviewers: epriestley, asherkin, btrahan
Reviewed By: btrahan
CC: aran, Korvin
Maniphest Tasks: T2189
Differential Revision: https://secure.phabricator.com/D4210