Catch errors that may occur whilst receiving data from the Aphlict server.

Summary: Ref T4324. Currently, if the AphlictMaster receives dodgy data from the Aphlict server (invalid JSON, for example) then a syntax error will be thrown and the AphlictMaster will die. Instead, catch errors and raise a notification.

Test Plan:

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4324

Differential Revision: https://secure.phabricator.com/D9380