Make view/sign page the primary Legalpad page

Summary:
  - Makes the "legal document" page the main page.
  - Links to the "manage" page.
  - The "manage" operation now requires CAN_EDIT.
  - Modernize some crumbs and such.

Test Plan: {F170213}

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D9733