Code refactorings

- Phoebe\Phoebe replaced by Phoebe\ConnectionManager
- Event bindings are now handled by Phoebe\Event\EventBinder class
(previously by Phoebe\Phoebe)
- Removed re-implementation of Phergie\Irc\Connection. Now
Phoebe\Connection extends it instead.
- Created small Phoebe\Event\EventDispatcherTrait which is used by
Connection and ConnectionManager
- EventDispatcher is now separated from Connection
- Added Phoebe\Timers (accessible by Event::getTimers() method)
- Fixed dependencies in composer.json
- Updated README.md according to updates