R1:b32a00dbace4

Update Legalpad for EditEngine

Summary: Updates Legalpad to use EditEngine, paving the way for //transaction comments//. Spooky.

Test Plan:
- New Document
- Require signing, Corp - see fail
- Require signing, Noone - see fail
- Require signing, Ind - get asked to sign
- Edit Document

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17862