Fix DB session problem in tests

[acidjunk]

Implementing delete.

Specs:

• Prices won't have delete for now (we work with a fixed 80 items product code)
• To make editing of Flavors and Effects easier a cascaded delete will be performed when you try to remove a Tag or Flavor (it will remove itself from all Product Kinds)
• Deleting a ProductKind will also delete active prices relations ships for it
• Deleting a Shop or a Category: will also delete active prices relations ships for it
• Rest of the endpoint will not cascade to be safer: just delete a record and fail when it has relation ships