GdaQuery and GdaCommand merge into GdaStatement

Previous Libgda versions proposed the GdaCommand and GdaQuery objects to execute SQL statements, with different features (GdaCommand was more generic but did not allow parameters bindings while GdaQuery allowed parameters bindings but could not execute some kind of problems)

Both of these objects have been removed and replaced by a new GdaStatement object which combines the features of both GdaCommand and GdaQuery. Most of the time GdaStatement object are created by GdaSqlParser objects. See this object's documentation for more information.