Add option to disable access to subscriptions (APP_WITH_SUBSCRIPTIONS)
Summary:
with small code improvements and tests
WARNING: This is on top of {D4304}
Test Plan: ./phpunit
Reviewers: #hkccp_developers, mollekopf
Reviewed By: #hkccp_developers, mollekopf
Subscribers: #hkccp_developers
Differential Revision: https://git.kolab.org/D4310