Copter: Split out prearm failures of low HDOP separately from !gps lock

(on the iris list there was some confusion on why the copter was blinking
yellow but yet they had gps lock)
Merge remote-tracking branch 'upstream/master'
Iris: Add Pitch Settings for gimbal
Remove unused .project file

This is apparently a eclipse .project file but it is not maintained
build: put px4io elf files in build directory
Rover: fixed logs directory
HAL_SITL: fixed GPS delay off by one
autotest: removed px4io loading instructions
Plane: initialise scheduler callback after logging

this could cause log corruption otherwise
Rover: initialise scheduler callback after logging

prevents possible log corruption
INS: replace APM with vehicle in accel calibrate
Copter: replace APM with board in cli
Rover: replace APM with board in cli
Plane: replace APM with board in cli
Plane: break up GPS and logging, allow GPS update at 50Hz

this prevents mismatches in GPS message arrival and accel message
arrival from causing small DCM errors
HAL_PX4: use larger buffers on USB
DataFlash: stop write logging while reading

prevents nuttx getting confused
GCS_MAVLink: sped up downloading DF logs over MAVLink
HAL_AVR: moved memcheck into HAL_AVR
AP_HAL: added available_memory() interface