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:

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

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