WIP: MAINT: refactor retrieve properties (move backend-logic to backend)

src/main/java/org/caosdb/server/entity/Entity.java

src/main/java/org/caosdb/server/entity/EntityInterface.java

src/main/java/org/caosdb/server/entity/wrapper/Domain.java

.../java/org/caosdb/server/entity/wrapper/EntityWrapper.java

src/test/java/org/caosdb/server/database/InsertTest.java

src/test/java/org/caosdb/server/database/InsertTest2.java