AP_Scripting: added applet SM_SwitchMission

[WillyZehnder]

Script for switching of missions that are saved on SD-card 'on the fly'.
Selection and loading can be done by one of two different methods (multi-position-switch or push-button).
The amount of missions is theoretically unlimited.
Convenient preparation of environment like searching sufficient table_key, finding correct sub-directory for SITL or SD-card and counting available and checking sufficient number of missions.

[timtuxworth]

What an absolutely brilliant idea!

[timtuxworth]

Perhaps "missions" should be at the APM root, rather than buried under "scripts"?

[WillyZehnder]

I would prefer to have the missions near scripts - but let's see what the developers strategy is.

[WillyZehnder]

What an absolutely brilliant idea!

Thank you Tim :o)

[IamPete1]

If it works and someone else can give it a try I'm happy to approve.

[WillyZehnder]

If it works and someone else can give it a try I'm happy to approve.

I tested a pre-version in real plane-flight and the latest version of course in SITL.
In the moment a real test of the latest version is not possible because of very nasty weather and 1°C(34°F).

The version without script-specific parameters is still commented by some users:
https://discuss.ardupilot.org/t/switch-missions-on-the-fly/92106/31

But I will ask for test-comments of the current version.

[WillyZehnder]

If it works and someone else can give it a try I'm happy to approve.

I improved it and tested the lua in SITL - all is working fine.
McKey tested it in Rover with positive feedback.
https://discuss.ardupilot.org/t/switch-missions-on-the-fly/92106/50

[WillyZehnder]

@IamPete1 Hi Pete, now all should be done.

[WillyZehnder]

After rebase, it seems the lua-bug of receiving a correct handle when opening a not existing file for reading is fixed.
But that leads to an error in my script because of using a nil-handle.
So I had to rework the script and could simplify the check after file:io.open.

[WillyZehnder]

https://discuss.ardupilot.org/t/switch-missions-on-the-fly/92106/58

@IamPete1 What else is necessary to merge (disregarding of a rebase)?

[IamPete1]

I have rebased, we now have a scripting check in CI which this will hopefully pass. If that passes and someone else has given it a go then I'm happy (I can give it a try here too at some point).

[WillyZehnder]

Thank you for rebase @IamPete1
"test scripting" passed
"I can give it a try here too at some point" - that would be great

[WillyZehnder]

I'm using that feature in nearly every flight with my gliders, especially with relocation+rotation, but it seems to me, nobody is really interested in it. I really wonder why.