Allow the Default/Backlog column to be renamed
Summary: Fixes T5101. There's no technical reason not to allow this, it just took a little extra work so I didn't do it originally.
Test Plan: Renamed "Backlog", un-renamed it. Tried to hide it.
Reviewers: chad
Reviewed By: chad
Subscribers: epriestley
Maniphest Tasks: T5101
Differential Revision: https://secure.phabricator.com/D9721