Add FEATURE FW_LAUNCH

[giacomo892]

This PR introduces the ability to enable NAV_LAUNCH as a feature.

It will allow to permanently enable Launch Mode without the needing of use a dedicated switch on the radio. The pilot with this feature just need to ARM and launch the plane according to the standard procedures.

• The pilot after having armed can leave Launch Mode by moving the ROLL/PITCH stick if the THROTTLE is LOW so the motor will behave depending if MOTOR_STOP is enabled or not. In this case the pilot can go for a manual launch.
• If the pilot inadvertently disarms the craft midair by placing THROTTLE to LOW, arming again (arming check) and just moving the sticks the Launch Mode will exit and full control will be given back to the pilot.

More cleanup and configurator support will come if you like the idea.

[shellixyz]

Nice. Would solve the in-flight disarm issue. Until recently I had the launch mode on a switch to prevent not being able to regain control. Now I'm not anymore I need my switch but I'm very very careful. It only happened to me once when I was using a RC glove and inadvertently disarmed just after launch but it has led to major damage. Having said that using #2331 is perhaps a better solution if it can be done.

[giacomo892]

@shellixyz Main goal of this PR, beside adding a security feature, is to make Launch Mode usage faster and easier and frees a switch on the radio too.
I use Launch Mode 100% of the times when I launch my wing and having to toggle a switch every time, and toggle back during flight is annoying :)
I simply like Launch Mode since the plane steady climbs leaving time to take a chair and wear googles and then you can take safely control of the plane when it is already at a safe altitude (clear of obstacles). Indeed when we will have flying/not flying detection it will be just easy to add another security check :)

[shellixyz]

Indeed launch mode is great I'm using it all the time. It makes the launch easy and also prevents the I term windup experienced when launching using stabilized modes.

I already enable it all the time now without a switch by using the full range of a channel but having it as a feature is nicer.

[digitalentity]

@DzikuVx @fiam what do you think? Looks good to me

[DzikuVx]

@digitalentity yes I think it is fine