Adds 'ACTIVE' as a valid channel state to indicate that the channel is

actively decoding, but no call or data is being transmitted.  This is
primarily used for P25 channels when TDU Link Control messages are
being transmitted in between voice or data transmissions on a channel.

Updated several of the P25 decoder state message processing sections to
keep the channel state UI updated with current call identifiers and
states.

Hard-coded channel state colors to remove inefficiency in the way that
channel state coloration was being handled.

src/main/java/io/github/dsheirer/channel/state/ChannelState.java

@@ -303,6 +303,11 @@ public class ChannelState extends Module implements ICallEventProvider, IDecoder
         {
             switch(state)
             {
+                case ACTIVE:
+                    broadcast(SquelchState.SQUELCH);
+                    updateFadeTimeout();
+                    mState = state;
+                    break;
                 case CONTROL:
                     //Don't allow traffic channels to be control channels, otherwise they can't transition to teardown
                     if(isStandardChannel())