Storage

**WIP** . Maybe a starting point for the Storage Part? Some things are already done
- [x] Add services definition
- [x] Create External Storage Class 
- [x] Create Storage Gateway Class
- [x] Implement getFieldData method for price
- [ ] Implement storeFieldData method
- [ ] Implemente deleteFieldData method

Let me know how this looks. 
`ez_is_field_empty`