* accounts: moved admin form model to forms.py and use of MyModelAdmin in order to distinct form from add form
* common: added MyModelAdmin, Image: if slug field doesnt exist in contenttype then use object_id
* customers: added image support + add form in order to hide non needed field at creation step
* suppliers: added add form to suppliers models in order to hide non-needed field at creation step, created entry + order classes in order to manage suppliers orders