[alpha.3] defaultValue no longer working

[natrim]

Seems like after rewrite to final-form

the defaultValue on SimpleForm and TabbedForm no longer works

and initialValues is not defined as prop, nor mentioned in docs

[djhi]

Right.. I wonder how we should handle this as final-form does not support defaultValue.

I think we should retrieve both initialValues and defaultValue, then:

• use only initialValues if both are defined, with a warning about defaultValue being deprecated and that it will be overridden by initialValues
• pass defaultValue as initialValues to final-form if defaultValue was the only one defined

[fzaninotto]

Fixed by #3756