Tracker: add arming library to avoid segmentation fault

Places make assumptions that the AP_Arming singleton is non-null

AntennaTracker/AP_Arming.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <AP_Arming/AP_Arming.h>
+
+// this class isn't actually used by Tracker; it's really just here so
+// the singleton doesn't come back as nullptr
+class AP_Arming_Tracker : public AP_Arming
+{
+public:
+    friend class Tracker;
+
+private:
+
+};

AntennaTracker/Tracker.h

@@ -52,6 +52,8 @@
 #include "GCS_Mavlink.h"
 #include "GCS_Tracker.h"
 
+#include "AP_Arming.h"
+
 #ifdef ENABLE_SCRIPTING
 #include <AP_Scripting/AP_Scripting.h>
 #endif
@@ -230,6 +232,9 @@ private:
     void tracking_manual_control(const mavlink_manual_control_t &msg);
     void update_armed_disarmed();
 
+    // Arming/Disarming management class
+    AP_Arming_Tracker arming;
+
     // Mission library
     AP_Mission mission{
             FUNCTOR_BIND_MEMBER(&Tracker::start_command_callback, bool, const AP_Mission::Mission_Command &),