AP_Mission: 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_Mission/AP_Mission_Commands.cpp

@@ -7,6 +7,7 @@
 #include <AP_ServoRelayEvents/AP_ServoRelayEvents.h>
 #include <AC_Sprayer/AC_Sprayer.h>
 #include <AP_Scripting/AP_Scripting.h>
+#include <RC_Channel/RC_Channel.h>
 
 bool AP_Mission::start_command_do_aux_function(const AP_Mission::Mission_Command& cmd)
 {