QSqlQueryModel: Provide a way to refresh/re-execute the current query

If it is possible for a database's contents to be modified externally (say, by a different client connected to the same SQL server), then it would be useful if the QSqlQueryModel could re-execute its query to fetch the updated data.

This can be achieved with the current API like this...

model->setQuery(model->query().executedQuery());

...but it would be nice to have a cleaner API like:

model->refreshQuery();