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

...n/java/org/caosdb/server/database/BackendTransaction.java

src/main/java/org/caosdb/server/database/DatabaseUtils.java

src/main/java/org/caosdb/server/database/Replacement.java

...end/implementation/MySQL/MySQLInsertEntityProperties.java

.../backend/implementation/MySQL/MySQLRegisterSubDomain.java

...tabase/backend/interfaces/InsertEntityPropertiesImpl.java

...er/database/backend/interfaces/RegisterSubDomainImpl.java

.../database/backend/transaction/InsertEntityProperties.java

...database/backend/transaction/InsertEntityTransaction.java

...erver/database/backend/transaction/RegisterSubDomain.java

...n/java/org/caosdb/server/database/proto/FlatProperty.java

.../java/org/caosdb/server/database/proto/ProtoProperty.java

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

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