Allow shop owner to control shop specific product types

TD:
add additional SHOP_CODE property to ProductType entity.
modify impex descriptors to account for this value.

General rule is:
1) if the shop_code is blank then this is a global type and it ca be seen by all but modified by sysadmin only
2) if the shop_code is filled in then only shop admins for that shop (and sysadmins) can see and modify this type