Simulated copter is flying too high and causing the land to timeout

Based on work by Jon Challinger (see earlier commit)

This allows the GCS to display to the user where the vehicle is flying
to in RTL and Guided flight modes

This reduces the chance that a forgotten rally point will cause the
vehicle to RTL to a distant location because instead it will RTL to
home.

RGB LED will remain flashing blue when vehicle is disarmed and this
check has failed (i.e. false).

Also changed mode_allows_arming function to accept arming_from_gcs param
Also remove AUTOTUNE from arming list