AP_Scripting:Add parameter controller applet

[Hwurzburg]

depends on #22438 dirlist binding and can run at the same time

[peterbarker]

@Hwurzburg this looks fine - was there some reason we haven't pushed forward with this one?

[Hwurzburg]

completely forgot about it....you CAN do this with three scripts and the script selector applet, but this is easier and does not require someone to write a script....I'll mark it for devcall to discuss

[IamPete1]

I have rebased so the new scripting autotest will run.

[timtuxworth]

What a great idea!

[peterbarker]

Can be merged after change to set rather set_and_save