Tuner Controller update to better handle automatic center frequency

calculation when additional channels are allocated.

Incorporates tuner specific definition of overall usable bandwidth, so
that tuners like airspy can specify 90% of 10 MHz (ie 9 MHz) is truly
usable and the fringe 10% is unusable rolloff.

Also includes tuner-specific defining of the width of the central spike,
or a value of 0 indicates that the entire range is usable (ie airspy).

src/spectrum/SpectralDisplayPanel.java

@@ -28,6 +28,7 @@ import java.awt.event.MouseEvent;
 import java.awt.event.MouseWheelEvent;
 import java.text.DecimalFormat;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Hashtable;
 
 import javax.swing.JCheckBoxMenuItem;