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