Copter: removed some unnecessary fields in GCS.h

save some memory
Rover: use common GCS.h
Copter: moved GCS.h to common library
Plane: use common GCS.h
GCS_MAVLink: import new mavlink XML
GCS_MAVLink: re-generate MAVLink headers
GCS_MAVLink: started adding MAVLink log download
DataFlash: added functions for load download support
Plane: moved ap_message into GCS.h
Copter: moved ap_message into GCS.h
Rover: moved ap_message into GCS.h
GCS_MAVLink: new headers for log download
GCS_MAVLink: support erase and faster downloads
Plane: enable new log download functions
Rover: support log download over MAVLink
Copter: support MAVLink log download
DataFlash: added structures to Init() of dataflash

this will allow the get_log_data() call to add FMT headers if a log
has wrapped
DataFlash: auto-add FMT headers to binary logs if needed

this copes with dataflash wrapping
GCS_MAVLink: prevent valgrind warnings on unfilled data
Plane: changes for new DataFlash API