setFetchSize and setMaxRows can't be configured

At $WORK, we ran into an issue with the Zeppelin JDBC interpreter whereby large SQL queries take ages to execute and actually bring the Zeppelin web interface to a halt. We eventually traced the problem down to the JDBCInterpreter.java file and these two lines:

// fetch n+1 rows in order to indicate there's more rows available (for large selects)
 statement.setFetchSize(getRowsFetchSize());
 statement.setMaxRows(getMaxRows() + 1);

It would be really cool if these two values could be set via the interpreter/jdbc/interpreter-setting.json file. I'm going to try to come up with a PR.