Resolves #96

Adds capability to disable spectral display.

Adds right-click context
menu items to disable display and/or reenable display by selecting
another tuner.

Adds view menu items to disable spectral display or show a tuner.

Persists spectral display enabled state across application run sessions.

src/main/java/io/github/dsheirer/spectrum/OverlayPanel.java

@@ -342,6 +342,10 @@ public class OverlayPanel extends JPanel implements ChannelEventListener, ISourc
         {
             minor = 1;
         }
+        if(label == 0)
+        {
+            label = 1;
+        }
 
         //Adjust the start frequency to a multiple of the minor tick spacing
         long frequency = minFrequency - (minFrequency % minor);