Allow providing initial data in ModelForm Meta

[Luoxzhg]

Now, we can specify 'widgets', 'labels', and so on in ModelForm's Meta innerclass and modelform_factory. But We can't specify 'initials' in Meta and modelform_factory. We must provide initial values in explicitly defined fields or in ModelForm instantiation.

class Person(models.Model):
    first = models.CharField(max_length=10)
    last = models.CharField(max_length=10)

class PersonForm(forms.ModelForm):
    last = forms.CharField(max_length=10, required=True, initial="Smith")
    class Meta:
        model = Person
        fields = '__all__'

If we can specify initial values in Meta, it is easier to specify initial values:

class PersonForm(forms.ModelForm):
    class Meta:
         model = Person
         fields = '__all__'
         initials = {'last': 'Smith'}

[Tim Graham]

We aren't going to add more and more override options in Meta. The decision from #20000: "It's understood that we have to draw a line somewhere, else we would have field definitions in the Meta, but I believe that line should be drawn at "anything cosmetic" available through Meta overrides, and "anything functional" through fields overrides."