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/channel/state/State.java

@@ -109,6 +109,17 @@ public enum State
 
     public abstract boolean canChangeTo(State state);
 
+    /**
+     * Indicates that this state is an active (ie decoding) state and is one of the states
+     * enumerated in the CALL_STATES enumeration set.
+     *
+     * @return true if this state is an active state
+     */
+    public boolean isActiveState()
+    {
+        return CALL_STATES.contains(this);
+    }
+
     public String getDisplayValue()
     {
         return mDisplayValue;