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/module/ProcessingChain.java

@@ -538,6 +538,9 @@ public class ProcessingChain implements IChannelEventListener
                     module.reset();
                 }
 
+                //Setup the channel state to monitor source overflow conditions
+                mSource.setOverflowListener(mChannelState);
+
 				/* Register with the source to receive sample data.  Setup a 
 				 * timer task to process the buffer queues 50 times a second 
 				 * (every 20 ms) */
@@ -606,6 +609,7 @@ public class ProcessingChain implements IChannelEventListener
             if(mSource != null)
             {
                 mSource.stop();
+                mSource.setOverflowListener(null);
 
                 switch(mSource.getSampleType())
                 {