Cockpit should offer to the user the option to send a "blank" state of MANUAL_CONTROL while on background

[rafaellehmkuhl]

We already have an option to persist the last joystick state, but this is usually not used because if the user goes to background while pressing a button or pushing a stick, this command will persist, and the vehicle can go crazy (e.g.: spinning, going up, descending, etc).

An option to keep sending a "zeroed" state could help.