Clean up some Phame transaction edit bugs

Summary: Ref T12685. Sets required on required fields, cleans up mailtags on PhamePost

Test Plan: Create a new blog, post.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12685

Differential Revision: https://secure.phabricator.com/D17850