Get rid of autoload in favor of explicit requires

Along the way this also fixed some other previously masked bugs:

* PunchblockPlugin was defined as inheriting from Plugin in one place and not another
* At least three classes never existed and were never referenced, but were made available via autoload:
  - Adhearsion::CallController::MenuDsl::Exceptions
  - Adhearsion::Dispatcher
  - Adhearsion::Plugin::Configuration
Maybe move that repetition of `adhearsion/` down here?