Update admin.py

RemovedInDjango18Warning: Options.module_name has been deprecated in favor of model_name
Merge pull request #355 from skipp/patch-1

Update admin.py deprecated RemovedInDjango18Warning
Refs #339 Readonly fields get displayed incorrectly in History view

Instead of passing the Version parameters as initial, override them in the object itself.
Works only for objects and not for inlines.