…properties and added .env to gitignore.

…er (#14)

* Add Order, OrderItem entities, and Status enum.

* Added repository and dto layers, added mappers for related Order & OrderItem entities.

* Added liquibase change files to create orders and order-items tables in DB. Fixed checkstyle issues.

* Added service and controller layers. Code refactored. Fixed issue in ShoppingCartRepository with findByUser query.

* Resolved issues:
 - Refactored order saving method in OrderServiceImpl.
 - Fixed issues with lazy initialization.
 - Added authorized user in the getOrderItem method in the controller so that any user cannot get another user's data.
 - Added equals & hashcode, and toString in OrderItem entity.
 - Added equals and hashcode to all entities.
 - Resolved issue when anyone can search for any order items.

* Resolved issue with shopping cart: now when an order is placed, the shopping cart is removed. Removed soft delete in ShoppingCart

* Fixed the issue where categories were not being added to saved books.

* Added exclude constraint for EqualsAndHashcode and ToString annotations. 
* Added @CreationTimestamp for orderDate in Order entity.

…re. Added Docker dependency in pom.xml.