Add Priority to Maniphest Hovercard

Summary: Fixes T5524, adds priority to Maniphest's hovercard. Also fixes Blocking language.

Test Plan: Hover over a task, see new stuff.

Reviewers: lpriestley, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5524

Differential Revision: https://secure.phabricator.com/D13750