fix position hold logic

do not set position setpoint too early

Home on takeoff

This reverts commit e0e7a241.

Commander: prevent the user from arming the system with USB

run preflight checks after mode switch has changed

Logging rate was limited to 1 Hz

I set the maximum to 100 Hz, since most SD cards are not fast enough for more. (but more is still possible with forcing)

Commander: Disarm after 5 seconds on the ground.