Add ordering to newforms classes

[David Cramer]

I'd like to propose adding an ordering attribute to a Meta class in newforms to allow overriding the field ordering for things like as_p.

e.g.

class Form:
    name = Char
    text = Char

    class Meta:
        ordering = ('text', 'name')

[James Bennett]

Duplicate of #5986, which has several proposals and recent activity.