Added pod Doc + 2 new subroutines for more comfortable get data set (wrappers)

The 2 new subroutines are:
*  get_single_value_from_db( $session, $table, $column, $id )
*  get_single_row_from_db( $session, $table, $id )

And make it much easier to use getDataSet(), also they do all the error handling and 
send helping log messages.
\+ they are  documented with POD.