Switch from array to TechDivision\Storage\StorageInterface for TimerServiceInterface::getTimers() and TimerServiceInterface::getAllTimers() methods 

* Bugfix for invalid serialize/unserialize methods in ScheduleExpression
* Add missing exeptions to TimerInterface doc block
* Add NoMoreTimeoutsException that indicates that a calendar-based timer will not result in any more timeouts
* Add bootstrap.php + phpunit.xml