Changes

The general architectural idea is to start the Flow with a TraceSource, allow the connection of multiple preprocessing modules (that are both: ActiveTraceObserver and TraceSource) and end the chain in an a TraceObserver (that can be a widget or an AnalysisSource). The sigTracesChanged signal (in the TraceSource objects) is used to propagate this notification through the chain and activate a callback method (processTraces) in the ActiveTraceObserver objects (like the WaveFormWidget) to read the new data. The PassiveTraceObservers (like the AnalysisSource and the TraceRecorder widget) will ignore this signal, so the processSignal() should be called manually.