[FEATURE] Create generic abstracts and interfaces for repositories and services

[Marco-Sulla]

Even if the code is auto-generated, is cumbersome that the same code is copy-pasted very much time.
I think it's better to implement a AbstractRepository and an Repository interface, that shares the common code to all repositories created with EWA. This abstract and interfacecan be useful also to people that do NOT want to use EWA. The same think should be done also for services.

For this reason, the findByNameOfUniqueId() must be renamed simply findById(). This also improves abstraction and encapsulation. Interface for models and aggregators should also be implemented.

PS: are specific interfaces for repo and services really needed? Evaluate to eliminate them.