Add project tags to PonderQuestion

Summary: T2628, adding project tags to ponder questions

Test Plan: Create ponder question, add project tag, save, project tag should show in question properties on question view.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D9447