Update Conpherence CSS to handle multiple edits better

Summary: Fixes T7655. We'll set tighter spacing around edit clusters. Also darkened up the date marker and remove unused phabricator-transaction-view CSS that was still scattered around the site.

Test Plan: Test a full and column multi-edit spam. Visited Ponder and Diffusion, noticed no issues using those apps. Grepped for other users of phabricator-transaction-view

Reviewers: epriestley, btrahan

Reviewed By: btrahan

Subscribers: Korvin, epriestley

Maniphest Tasks: T7655

Differential Revision: https://secure.phabricator.com/D12148