Better way to get Fomik form values

Currently, we pass a ref to the `Formik` component explicitly. That ref is being assigned to `FormikProps`. We need a helper `getFormikProps` which accepts a `ReactWrapper` (provided by `enzyme`) pointing to `Formik` component, and return `FormikProps`.
The usage should be:
```tsx
const wrapper = mount(...)
const formikProps = getFormikProps(wrapper.find(Formik))
```
Ideas:
Figure out how to get `value` from a context provider outside of its child tree.