Prompt to adding a project if none in Maniphest

Summary: Adds 'Add Project...' if no projects present on Maniphest items. Also - I can't seem to get a dialog to pop, what am I missing? Fixes T3308

Test Plan: Click add project, get edit form.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3308

Differential Revision: https://secure.phabricator.com/D6121