R1:200b51df5d9a

Set a default paste header

Summary: Fixes T4040

Test Plan: Create new paste without title, see title.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4040

Differential Revision: https://secure.phabricator.com/D7605