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/tuner/airspy/AirspyTuner.java

@@ -0,0 +1,168 @@
+package source.tuner.airspy;
+
+import java.util.concurrent.RejectedExecutionException;
+
+import javax.swing.JPanel;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import sample.Listener;
+import sample.complex.ComplexBuffer;
+import source.SourceException;
+import source.tuner.Tuner;
+import source.tuner.TunerChannel;
+import source.tuner.TunerChannelSource;
+import source.tuner.TunerClass;
+import source.tuner.TunerConfiguration;
+import source.tuner.TunerType;
+import source.tuner.airspy.AirspyTunerController.BoardID;
+import controller.ResourceManager;
+import controller.ThreadPoolManager;
+
+/*******************************************************************************
+ *     SDR Trunk 
+ *     Copyright (C) 2015 Dennis Sheirer
+ * 
+ *     This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ * 
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ * 
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program.  If not, see <http://www.gnu.org/licenses/>
+ ******************************************************************************/
+public class AirspyTuner extends Tuner
+{
+	private final static Logger mLog = LoggerFactory.getLogger( AirspyTuner.class );
+
+	AirspyTunerController mController;
+	
+	public AirspyTuner( AirspyTunerController controller )
+	{
+		super( "Airspy" );
+		
+		mController = controller;
+		
+		/* Register for frequency/sample rate changes so that we can rebroadcast
+		 * to any registered listeners */
+		mController.addListener( this );
+	}
+	
+	@Override
+	public JPanel getEditor( ResourceManager resourceManager )
+	{
+		return new AirspyTunerEditorPanel( this, resourceManager );
+	}
+	
+	public AirspyTunerController getController()
+	{
+		return mController;
+	}
+
+	@Override
+	public void apply( TunerConfiguration config ) throws SourceException
+	{
+		mController.apply( config );
+	}
+
+	@Override
+    public String getUniqueID()
+    {
+		try
+		{
+			return mController.getDeviceInfo().getSerialNumber();
+		}
+		catch( Exception e )
+		{
+			mLog.error( "error gettting serial number", e );
+		}
+		
+		return BoardID.AIRSPY.getLabel();
+    }
+
+	@Override
+	public TunerClass getTunerClass()
+	{
+		return TunerClass.AIRSPY;
+	}
+
+	@Override
+	public TunerType getTunerType()
+	{
+		return TunerType.AIRSPY_R820T;
+	}
+
+	@Override
+	public int getSampleRate()
+	{
+		int rate = 0;
+		
+		try
+		{
+			rate = mController.getCurrentSampleRate();
+		} 
+		catch ( SourceException e )
+		{
+			mLog.debug( "Error while getting sample rate from controller", e );
+		}
+		
+		return rate;
+	}
+	
+	@Override
+	public double getSampleSize()
+	{
+		return 12.0;
+	}
+
+	@Override
+	public long getFrequency() throws SourceException
+	{
+		return mController.getFrequency();
+	}
+
+	@Override
+    public TunerChannelSource getChannel( ThreadPoolManager threadPoolManager,
+		TunerChannel channel ) throws RejectedExecutionException, SourceException
+    {
+		//TODO: this channel has a decimated sample rate of:
+		// 10.0 MSps = 10,000,000 / 208 = 48076.923
+		//  5.0 MSps =  5,000,000 / 104 = 48076.923
+		//  2.5 MSps =  2,500,000 /  52 = 48076.923
+		//Consider implementing a fractional resampler to get a correct 48 kHz
+		//output sample rate
+		
+	    return mController.getChannel( threadPoolManager, this, channel );
+    }
+
+	@Override
+    public void releaseChannel( TunerChannelSource source )
+    {
+		/* Unregister for receiving samples */
+		removeListener( (Listener<ComplexBuffer>)source );
+		
+		/* Tell the controller to release the channel and cleanup */
+		if( source != null )
+		{
+			mController.releaseChannel( source );
+		}
+    }
+
+	@Override
+	public void addListener( Listener<ComplexBuffer> listener )
+	{
+		mController.addListener( listener );
+	}
+	
+	@Override
+	public void removeListener( Listener<ComplexBuffer> listener )
+	{
+		mController.removeListener( listener );
+	}
+}