Replace context bar in Maniphest with PHUIInfoView

Summary: Removes AphrontContext bar and uses PHUIInfoView instead. This also attaches to the ObjectBox instead for cleaner UI. Also moved phui-error-view.css which was missed.

Test Plan: Test creating a subtask or a new task, see updated info bar and action buttons.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11920