Implement Library Specification API interfaces

- Define the interfaces for the Scheduler domain objects.
  - Configuration
  - ThreadPool
  - SchedulerFactory
  - Scheduler
  - Job
  - Trigger
    - Simple
    - Cron
  - JobCallback
  - JobCallbackFactory
  - JobExecutionContext
  - SchedulerException
  - SchedulerListener
  - JobListener
  - TriggerListener
