AI: Added Drag Race and Crash driving modes, fixes and UI improvements

[tritonas00]

• A new Drag Race mode added which auto configures the settings and makes possible to select two vehicles to perform a drag race. Returning to other modes preserves the previous selections.

Just two waypoints making a line are enough for this mode.

• A new Crash driving mode added which auto configures the settings and makes possible to select two vehicles to perform a crash. Returning to other modes preserves the previous selections.

Again just two waypoints making a line are enough for this mode.

• Fixed setting sectionconfig when skin is also available

• Moved driving mode on top

• Don't allow changing mode when AI is running

• If no preset found, show supported terrains list also (fetchable from json)

• Prefer local file savegames/waypoints.json if exists

[tritonas00]

Don't allow changing mode when AI is started

i might redo this -> check if any AI origin actor is loaded

[ohlidalp]

I took the liberty to mark this PR 'draft' and un-request my review. I've almost started reviewing several times and the branch always evolved more! Not that I'm complaining.

[tritonas00]

Hehe, indeed. I will notify you when im really done.

[tritonas00]

@only-a-ptr is it ok to merge?

[ohlidalp]

Purpose: to have fun!

Estimate: I think it's ready to be merged anytime, and even if not, it'll be ready in 1 man day (8 hrs).

Work to be done: I'll test it today.