Speedometer show total kart

[dumaosen]

https://github.com/supertuxkart/stk-code/pull/4099
I made a PR recently, and it;'s revamped from an old branch of alayan's.
The difference is, it looks fit in >10 total karts and it's optional. It is defaultly disabled.

[QwertyChouskie]

I'd like to see a pic with 20/20 shown, as that is where things will feel more cramped. Anyways, having an option is nice, and at least the one picture given seems to look nice.

[Alayan]

That's the issue with this PR, the text gets quite small with 10+ karts.

[tempAnon093]

I'm quite neutral on it. I don't need to know how many other karts there are, and I usually know in advance (it usually won't change in a race). The current one gives me all the information I need without anything unnecessary.