Observer and Observable implementation to support "multiple loggers"

Resolved issue #24.

Added a base class for Observerables: ObservableBase
All available Agents (Auctioneer, Concentrator and PVPanelAgent) now extend the ObservableBase. This allows for automatic addition of Observers within the OSGI runtime.

Added a base class for Observers: ObserverBase
The ObserverBase class will function as a helper class to create an Observer. It has add and remove operations and controls a filter. The filter allows for selection of specific Observerables. The filter is optional: no filter will attach to all available Oberservables and a filter will only attach to specified Observables.

Added an example Observer: SimpleObserver
A simple example Observer is availble, demonstrating the minimal coding involed to create an Observer. The SimpleObserver will output all events received to a SLF4J logger.