[Redesign] Update Paste UI

Summary: Ref T8099, Adds a bit more color/contract to Paste.

Test Plan: Review a list of Pastes, embedded Pastes, and the main Paste UI.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8099

Differential Revision: https://secure.phabricator.com/D13083