Fix #275: Denote optional field more explicitely.

[n1k0]

Refs #275, WiP, cc @kav; patch deployed to gh-pages.

Denoting optional fields instead of required ones, as suggested in these UX guidelines for forms:

Edit: revamped the patch with better styling for optional fields. it now prevents the Form root schema field to be considered as optional:

Thoughts?

[n1k0]

As if doing this wasn't hard enough already, I asked my twitter followers about that; mixed feelings https://twitter.com/n1k0/status/752908241529483265

[n1k0]

Damn, this doesn't help

Maybe we should make it an option (no pun intended)?

[mplis-jetsetter]

In a form with both required and optional fields, I think both strategies work fine. You can argue over which looks better, but they both get the job done. The issues come into play when you have an all-required or an all-optional form.

I think there's definitely potential for confusion with a large all-required form if you're only denoting optional fields. I think the user is likely to not realize that all fields are required, attempt to submit an incomplete form, and be confused/frustrated by the error messages thinking "I didn't know that field was required".

In general, it just makes more sense to me to call out required fields. You're calling the user's attention to fields that require their attention instead of calling their attention to fields that don't require their attention.

[kav]

I think it will vary by use case and in some cases even form to form. See my pull for a bit more flexible alternative that doesn't make a value judgement here

[n1k0]

Now #304 has landed, one can easily override how labels are rendered. Discarding this.