Resolves #165 - P25 decoding channel stops arbitrarily and never recovers.

Issue identified with Patch Group management and circular dependencies that can develop because of stale patch groups.  Refactored all patch group management into a new PatchGroupManager.  Patch groups are now automatically deleted if we don't receive any update messages within 5 seconds.  The PatchGroupAlias was also updated to not roll-up attributes from subordinate patched group aliases when those aliases are also patch group aliases -- this eliminates the circular dependency chaining.

Added IOverflowListener interface and updated Sources to support overflow listeners.  Updated ChannelState to register as an overflow listener so that it can visually depict to the user when the channel enters/exits source overflow state.  Added new color pattern for OVERFLOW with yellow text on red.

src/source/tuner/usb/USBTransferProcessor.java

@@ -30,6 +30,7 @@ import sample.Listener;
 import sample.OverflowableTransferQueue;
 import sample.adapter.ISampleAdapter;
 import sample.complex.ComplexBuffer;
+import sample.real.IOverflowListener;
 import source.tuner.TunerManager;
 import util.ThreadPool;
 
@@ -101,12 +102,12 @@ public class USBTransferProcessor implements TransferCallback
         mBufferSize = bufferSize;
 
         mFilledBuffers = new OverflowableTransferQueue<>(FILLED_BUFFER_MAX_CAPACITY, FILLED_BUFFER_OVERFLOW_RESET_THRESHOLD);
-        mFilledBuffers.setStateListener(new Listener<OverflowableTransferQueue.State>()
+        mFilledBuffers.setOverflowListener(new IOverflowListener()
         {
             @Override
-            public void receive(OverflowableTransferQueue.State state)
+            public void sourceOverflow(boolean overflow)
             {
-                if(state == OverflowableTransferQueue.State.NORMAL)
+                if(overflow)
                 {
                     mLog.debug(mDeviceName + " - buffer overflow - temporary pause until processing catches up");
                 }