Refs #339 Readonly fields get displayed incorrectly in History view

Instead of passing the Version parameters as initial, override them in the object itself
I don't think that field.attname is correct here. FK fields have an attname of `"name_id"`, but are stored in serialised models as `"name"`

I think this can be simplified as:

```
for key, value in initial.iteritems():
    setattr(obj, key, value)
```