Update Phortune Merchant UI to bring it in line with Account UI

Summary:
Depends on D20732. Ref T13366. This generally makes the "Merchant" UI look and work like the "Payment Account" UI.

This is mostly simpler since the permissions have largely been sorted out already and there's less going on here and less weirdness around view/edit policies.

Test Plan: Browsed all Merchant functions as a merchant member and non-member.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13366

Differential Revision: https://secure.phabricator.com/D20733