Add interfaces to interact with subscription from support app

lib/composer/composer/autoload_classmap.php

lib/composer/composer/autoload_static.php

lib/private/Server.php

lib/private/Support/Subscription/Registry.php

...ort/Subscription/Exception/AlreadyRegisteredException.php

lib/public/Support/Subscription/IRegistry.php

lib/public/Support/Subscription/ISubscription.php

lib/public/Support/Subscription/ISupportedApps.php

tests/lib/Support/Subscription/RegistryTest.php