Added (a lots of) comments to code; unused methods cleanup

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

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

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

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

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

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

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

...re/src/main/java/it/inaf/ia2/tsm/datalayer/DBWrapper.java

...src/main/java/it/inaf/ia2/tsm/datalayer/DataTypeMode.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

...java/it/inaf/ia2/tsm/model/CommaSeparatedListAdapter.java

...re/src/main/java/it/inaf/ia2/tsm/model/DBTypeMapping.java

.../main/java/it/inaf/ia2/tsm/model/DataTypeModeAdapter.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

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

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