Move subscription updates to the `register` function.

Summary: Currently, the `AphlictClient` will only send its subscriptions to the `AphlictMaster` once. If the original `AphlictMaster` is closed and a new master is created, then client subscriptions will be lost.

Test Plan: Opened two separate tabs. Closed the "master" tab and noticed that the subscriptions were re-sent to the server.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9487