Clarify Subscription page language
Summary: This says "Edit Subscription" but the page only lets you update the payment method for autopay. I think this is confusing users. I tried to find the best language here, but suggest something else if you prefer.
Test Plan: Review language on sample subscription page.
Reviewed By: epriestley
Maniphest Tasks: T12451
Differential Revision: https://secure.phabricator.com/D17944