[schema] implements toString for Reference
[db] manage references indexation + CRUD storage
[db,schema]  fixed the find property in parent
[db,schema] use interface of storage instead of impl
[db,tests] add some tests for a reference
Merge branch 'sprint' of https://github.com/sleroy/komea into sprint

Conflicts:
	core/shared/komea-db-commons/src/main/java/org/komea/core/model/impl/OKomeaModelFactory.java
	core/shared/komea-db-commons/src/main/java/org/komea/core/schema/impl/EntityType.java
[db, schema] Primtive is now implementation of IType
[db,model] restore exception throw for unknown properties