RC_Channel: 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/RC_Channel/RC_Channel.cpp

@@ -36,6 +36,7 @@ extern const AP_HAL::HAL& hal;
 #include <AP_Gripper/AP_Gripper.h>
 #include <AP_ADSB/AP_ADSB.h>
 #include <AP_LandingGear/AP_LandingGear.h>
+#include <AP_Logger/AP_Logger.h>
 #include <AP_ServoRelayEvents/AP_ServoRelayEvents.h>
 #include <AP_Arming/AP_Arming.h>
 #include <AP_Avoidance/AP_Avoidance.h>