Add support for rotation direction parameter of MAV_CMD_CONDITION_YAW

This is the completion of an existing TO-DO in the code which adds support for the Mavlink parameter of MAV_CMD_CONDITION_YAW that determines what in direction yaw will occur. One complication was that Mavlink expects a value of -1 to indicate counterclockwise, but we are using an unsigned int for this parameter of the location struct so I figured we could just use 0, 1, and 2 to indicate default behaviour, clockwise, and counterclockwise, respectively.

It has been tested in SITL and didn't present any issues. I think it's ready for master.