Closes #71 - frequency controller throws exception when exceeding min/max tuning limits of a tuner.

Updated code to show dialog to user whenever the tuning limit has been exceeded.  Added new InvalidFrequencyException that includes the requested invalid frequency and the valid frequency limit that was exceeded

src/source/tuner/hackrf/HackRFTunerEditor.java

@@ -142,7 +142,7 @@ public class HackRFTunerEditor extends TunerConfigurationEditor
 					mController.setSampleRate( sampleRate );
 	                save();
                 }
-                catch ( UsbException e2 )
+                catch ( SourceException|UsbException e2 )
                 {
                 	JOptionPane.showMessageDialog( HackRFTunerEditor.this, "HackRF Tuner Controller"
             			+ " - couldn't apply the sample rate setting [" + sampleRate.getLabel() +