Adds airspy USB tuner support and updates the spectral display

component.

-Airspy supported with 10 and 2.5 MSps sample rates.  Additional
decimation may be added later.

-Spectral display updated to include smoothing and filtering options.

Note: the decimated output of a tuner channel from the airspy is
48,076.9 samples per second, versus the normal 48 kHz decimated rate.
This is 1.0015 times the normal rate and doesn't appear to impact the
decoders or audio processing.  Therefore, no fractional resampling has
been added.

src/source/mixer/RealMixerSource.java

@@ -31,7 +31,7 @@ import org.slf4j.LoggerFactory;
 
 import dsp.gain.AutomaticGainControl;
 import sample.Listener;
-import sample.adapter.SampleAdapter;
+import sample.adapter.ISampleAdapter;
 import sample.real.RealBuffer;
 import source.RealSource;
 import source.SourceException;
@@ -49,7 +49,7 @@ public class RealMixerSource extends RealSource
 	private AudioFormat mAudioFormat;
 	private String mDisplayName;
 	private int mBytesPerFrame = 0;
-	private SampleAdapter mSampleAdapter;
+	private ISampleAdapter mSampleAdapter;
 	private AutomaticGainControl mAGC = new AutomaticGainControl();
 	
 	CopyOnWriteArrayList<Listener<RealBuffer>> mSampleListeners = 
@@ -74,7 +74,7 @@ public class RealMixerSource extends RealSource
     public RealMixerSource( TargetDataLine targetDataLine, 
     						   AudioFormat format,
     						   String name,
-    						   SampleAdapter sampleAdapter )
+    						   ISampleAdapter sampleAdapter )
     {
     	super( name );