Move to permission based dashboard access

As PBD was realized in oscar's master branch i tried to adjust stores code. Staff user with limited dashboard access can view, add or edit, but cant delete stores information (i.e. to change work time or address). Also, she cant manage stores groups. This is an issue to discuss about, should that user to view store's info or not. Better way is to enhance model's logic by partner assignment feature. 
I will try to make it myself, but any advices will be helpful as i'm newbie in django/oscar/python and this is my first pull request :)