Refactoring of the Aphlict server

Summary: Tidy the Aphlict server by splitting the functionality into two main modules, AphlictClientServer and `AphlictAdminServer. There is still further tidying that could be done here, but I feel that this puts us in a much better place.

Test Plan: Sent notifications via /notification/status/.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11383