AfterInitializedHooks should be different than thread joining

Presently, the last step of initialization is to join a series of threads to prevent the Adhearsion process from ending prematurely. Each component within Adhearsion does this through an after-initialized hook. This prevents small after-initialized tasks from running reliably (such as printing that Adhearsion has indeed initialized).

Thread joining should be done absolutely last and, because it's conceptually different from a hook, should probably be handled separately.