AP_HAL: stop libraries including AP_Logger.h in .h files

AP_Logger.h is a nexus of includes; while this is being improved over
time, there's no reason for the library headers to include AP_Logger.h
as the logger itself is access by singleton and the structures are in
LogStructure.h

This necessitated moving The PID_Info structure out of AP_Logger's
namespace.  This cleans up a pretty nasty bit - that structure is
definitely not simply used for logging, but also used to pass pid
information around to controllers!

There are a lot of patches in here because AP_Logger.h, acting as a
nexus, was providing transitive header file inclusion in many (some
unlikely!) places.

libraries/AP_HAL/examples/DSP_test/DSP_test.cpp

@@ -3,6 +3,7 @@
 #include <GCS_MAVLink/GCS_Dummy.h>
 #include <AP_Vehicle/AP_Vehicle.h>
 #include <AP_SerialManager/AP_SerialManager.h>
+#include <AP_Logger/AP_Logger.h>
 #include "GyroFrame.h"
 
 #if HAL_WITH_DSP