EventAdmin shell commands and Event bean

- Event.__init__() can now be called without argument (and has a default topic).
  This is necessary to notify remote EventAdmin through RemoteServices

- Added a shell command component for event admin, adding the following commands:
  - send <topic> [<property=value> [...]] : sends an event with the given topic and properties (synchronous)
  - post <topic> [<property=value> [...]] : posts an event (asynchronous)