Dashboard panel for Maniphest tasks/groups

Summary: Basic styling for the 'panel' version of Maniphest groups. Not super sold on it, but a decent start.

Test Plan:
Test dashboards and Maniphest homepage

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{F157640}

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9219