321 - adds a preferred tuner option to the channel's source configuration

so that on startup, the application attempts to source the channel from
the preferred tuner.

If the tuner is currently not available, or if the tuner cannot source
the channel, then the next available tuner is selected.

src/main/java/io/github/dsheirer/source/config/SourceConfigTuner.java

@@ -69,6 +69,15 @@ public class SourceConfigTuner extends SourceConfiguration
         return mPreferredTuner;
     }
 
+    /**
+     * Indicates if this configuration has a specified preferred tuner
+     */
+    @JsonIgnore
+    public boolean hasPreferredTuner()
+    {
+        return mPreferredTuner != null;
+    }
+
     /**
      * Specifies the preferred tuner to use for this configuration
      * @param preferredTuner to use, if available