To event service are added:
  - 'Task' entity, and 'enqueue()' method to send 'Task' into queue.
  - 'Listener' entity and method 'createListener()'
Implementations of EventService and EventListener moved into Impl directory.
EventListener updated.
Finished previous commit.
Added ChannelSettings class

Added ChannelSettings class to support individual settings for each channel.
BaseEvent renamed to AbstractEvent, added required property channelType. Some refactoring.
Minor refactoring.
Merge pull request #2 from kavnik/master

Introduce an event listener support