WIP on "shipping address" form for paper books shipping

* Renamed Address Entity to "ShippingAddress"
* Renamed our "AdressType" form type to "ShippingAddressType"
* Added a events binding for books "order" / "shipping address submission" operations
* Added a DB migration & table schema (in MySQL Workbench) for our "shipping_address" table
* Removed the useless BookRepository, added a BookPaymentRepository
* Small i18n keys modifications
* Misc tiny updates (comments removal in previous DB migrations, LESS fine-tuning...)