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/hackrf/HackRFTunerController.java

@@ -142,8 +142,21 @@ public class HackRFTunerController extends TunerController
 	{
 		mDeviceHandle = new DeviceHandle();
 		
-		LibUsb.open( mDevice, mDeviceHandle );
+		int result = LibUsb.open( mDevice, mDeviceHandle );
 		
+		if( result != 0 )
+		{
+			if( result == LibUsb.ERROR_ACCESS )
+			{
+				mLog.error( "Unable to access HackRF - insufficient permissions.  "
+					+ "If you are running a Linux OS, have you installed the "
+					+ "hackRF rules file in \\etc\\udev\\rules.d ??" );
+			}
+			
+			throw new SourceException( "Couldn't open hackrf device - " +
+				LibUsb.strError( result ) );
+		}
+
 		try
 		{
 			claimInterface();
@@ -298,7 +311,7 @@ public class HackRFTunerController extends TunerController
 	 */
     public long getTunedFrequency() throws SourceException
     {
-		return 0;
+		return mFrequencyController.getTunedFrequency();
     }
 
 	@Override