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/TunerEvent.java

@@ -23,12 +23,13 @@ public class TunerEvent
 
     public enum Event
     {
-        ADD,
-        LOCK_STATE_CHANGE,
-        REMOVE,
         CHANNEL_COUNT,
-        FREQUENCY,
-        SAMPLE_RATE,
+        FREQUENCY_UPDATED,
+        FREQUENCY_ERROR_UPDATED,
+        LOCK_STATE_CHANGE,
+        MEASURED_FREQUENCY_ERROR_UPDATED,
+        SAMPLE_RATE_UPDATED,
+
         CLEAR_MAIN_SPECTRAL_DISPLAY,
         REQUEST_MAIN_SPECTRAL_DISPLAY,
         REQUEST_NEW_SPECTRAL_DISPLAY;