Resolves #373 - Adds support for Tuner frequency error PPM monitoring

and auto-correction for R820T tuners.

-Updated TunerModel and TunerViewPanel to add 2 new columns to
display the current tuner's PPM setting and (when available) the
measured frequency error averaged over 5 second intervals provided by
certain decoders (e.g. P25 C4FM and LSM).  Frequency error value from
P25 decoders is provided from the Costas Loop PLL once 2 or more P25
message sync events have been observed in a short period.
-Updated R820T tuner to auto-correct PPM when measured frequency error
exceeds the +/- 0.4PPM threshold for a period of 30 seconds or more.
Feature can be enabled/disabled by user in the tuner editor panel.

Resolved several issues with P25 C4FM/LSM decoders that was impacting
performance related to channel misalignment from tuner PPM offsets.

src/main/java/io/github/dsheirer/source/tuner/manager/TunerChannelSourceManager.java

@@ -459,6 +459,11 @@ public class TunerChannelSourceManager extends ChannelSourceManager
                 //when the polyphase manager has channels allocated
                 mTunerController.setLocked(getTunerChannelCount() > 0);
                 break;
+            case NOTIFICATION_MEASURED_FREQUENCY_ERROR_SYNC_LOCKED:
+                //Rebroadcast these frequency measurement errors to the tuner and tuner controller
+                //for display and/or correction
+                broadcast(sourceEvent);
+                break;
             default:
                 mLog.info("Unrecognized source event: " + sourceEvent);
                 break;