Consistency in form widget names

[Korbeil]

Was working with symfony/form and was using form widget names with snake_case.
I needed some help with a simple bug and @lyrixx told me that we should not use snake_case.

But since I saw snake_case from the docs and I also saw camelCase I just made a pass to have camelCase everywhere for form widget names.

[OskarStark]

Was the bug related to snake_case/camelCase?

[Korbeil]

I made a DTO witch camelCase attributes (like every class we usely do) and my form having snake_case widget names so error mapping was incorrect :/ So kind of yes.
The idea is just to enforce people using camelCase to have correct error mapping 😉

[javiereguiluz]

@Korbeil thank you ... and congrats on your first Symfony Docs contribution! We merged it in 3.4 branch and then we'll merge it in the other branches.