Resolves #170 adding support for Airspy Mini tuner's 3 and 6 MHz

sample rates.

Resolves issue in PolyphaseChannelManager responding to sample rate
changes in the tuner.  The manager now recreates the channelizer when
needed if the tuner's sample rate has changed since the last time the
channelizer was used.

Updates the Tuner selection view to reflect tuner lock state.  Updates
the tuner editors to enable/disable frequency controller and sample
rate controls according to the tuner's lock state.

src/main/java/io/github/dsheirer/gui/control/JFrequencyControl.java

@@ -125,6 +125,8 @@ public class JFrequencyControl extends JPanel implements ISourceEventProcessor
         mBlankCursor = Toolkit.getDefaultToolkit()
             .createCustomCursor(cursorImage, new Point(0, 0), "cursor");
 
+        setTooltip(false);
+
         revalidate();
     }
 
@@ -139,6 +141,26 @@ public class JFrequencyControl extends JPanel implements ISourceEventProcessor
         }
     }
 
+    private void setTooltip(boolean locked)
+    {
+        String tooltip = null;
+
+        if(locked)
+        {
+            tooltip = "Frequency control is locked.  Disable decoding channels to unlock.";
+        }
+        else
+        {
+            tooltip = "Click on a frequency digit and type a frequency value, or click the upper/lower digits to " +
+                "change the value";
+        }
+
+        for(Digit digit: mDigits.values())
+        {
+            digit.setToolTipText(tooltip);
+        }
+    }
+
     /**
      * Receives a frequency change event invoked by another control.  We don't
      * rebroadcast this event, just set the control to indicate the new frequency.
@@ -165,6 +187,7 @@ public class JFrequencyControl extends JPanel implements ISourceEventProcessor
                     public void run()
                     {
                         setEnabled(false);
+                        setTooltip(true);
                     }
                 });
                 break;
@@ -175,6 +198,7 @@ public class JFrequencyControl extends JPanel implements ISourceEventProcessor
                     public void run()
                     {
                         setEnabled(true);
+                        setTooltip(false);
                     }
                 });
                 break;