Fixed PageField to work with Django 1.7

When migrations call ForeignKey.deconstruct, it manipulates the `to` argument in kwargs.
Changed this to use `to` in kwargs instead of hard coding so migrations work.
`limit_choices_to` is not a valid kwarg for forms.MultiValueField
Merge pull request #3500 from jsma/pagefield-fix

Fixed PageField to work with Django 1.7