Allow configuration of default document policies for Legalpad
Summary: Ref T3116. User request / generally modern feature.
Test Plan: Set defaults to whacky projects and created a new document; it defaulted appropriately.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran, allan.laal
Maniphest Tasks: T3116
Differential Revision: https://secure.phabricator.com/D8110