Lockdown disable

This PR allows to disable the HIL actuator lockdown on actuators. Currently only supported in PX4IO, and requires to complete a command line dialog.

Since this is so frickin' dangerous non-console enable support will *NOT* be accepted in mainline. The command looks like this and requires confirmation with 'y' to proceed. It will time out in 5 seconds.

```
nsh> px4io lockdown disable
px4io: WARNING: ACTUATORS WILL BE LIVE IN HIL! PROCEED?
px4io: Press 'y' to enable, any other key to abort.
px4io: WARNING: ACTUATORS ARE NOW LIVE IN HIL!
```