SITL: added SIM_GPS_TYPE control

for choosing what sort of GPS to simulate
SITL: added simulation of the original MTK GPS
SITL: added support for MTK16 and MTK19 simulated GPS types
SITL: improve time field handling in simulated GPS
SITL: added SIM_GPS_BYTELOSS option

this allows testing of protocol recovery after losing bytes on the GPS
serial link
AP_GPS: removed the old MTK16 driver

the MTK19 driver supports both the 1.6 and 1.9 protocol
HAL_PX4: enable ttyACM0 as main console, ttyS1 as telemetry port
HAL_PX4: perform automatic update of px4io firmware
Plane: enable PX4IO dual telemetry devices
HAL_PX4: cope with O_NONBLOCK not working in NuttX on ttyACM0

writes will block anyway, which clags up APM
AP_InertialSensor: return roll and pitch trim angles
Copter: integrate automatic roll and pitch trims
Plane: integrate automatic roll and pitch trims
Rover: integrate automatic roll and pitch trims
Copter: update firmware version to 2.9.1-rc1
Copter: updated release notes for 2.9.1-rc2
Copter: update version to 2.9.1 ahead of release
AHRS: limit trim to 10 degrees
AHRS: fix example sketch to use roll/pitch trim
Plane: fixed a bug with setting stream rates 

this is what caused the "no sensors" problem in the 2.69 release