Improvements on XML models inheritance (in progress)

TASMAN-core/src/main/java/it/inaf/ia2/tsm/Column.java

...AN-core/src/main/java/it/inaf/ia2/tsm/EntityProperty.java

TASMAN-core/src/main/java/it/inaf/ia2/tsm/Table.java

TASMAN-core/src/main/java/it/inaf/ia2/tsm/TapSchema.java

...N-core/src/main/java/it/inaf/ia2/tsm/TapSchemaEntity.java

...ore/src/main/java/it/inaf/ia2/tsm/datalayer/DBBroker.java

...main/java/it/inaf/ia2/tsm/datalayer/DBBrokerTemplate.java

...n/java/it/inaf/ia2/tsm/datalayer/mysql/MySQLDBBroker.java

...ava/it/inaf/ia2/tsm/datalayer/pgsql/PostgresDBBroker.java

...core/src/main/java/it/inaf/ia2/tsm/model/ColumnModel.java

...ain/java/it/inaf/ia2/tsm/model/ModelLoadingException.java

...core/src/main/java/it/inaf/ia2/tsm/model/SchemaModel.java

...ore/src/main/java/it/inaf/ia2/tsm/model/SchemaModels.java

...e/src/main/java/it/inaf/ia2/tsm/model/SchemaXMLModel.java

...-core/src/main/java/it/inaf/ia2/tsm/model/TableModel.java

...ore/src/main/java/it/inaf/ia2/tsm/model/TypesMapping.java

...N-core/src/main/java/it/inaf/ia2/tsm/model/XMLMerger.java

.../src/main/java/it/inaf/ia2/tsm/model/XMLModelsLoader.java

TASMAN-core/src/main/resources/core.properties

...AN-core/src/main/resources/schema_definition/ivoa-1_1.xml