master
move task 2033, 5108, 6956, 7225 to separate practice remove task6981 because it don't add value remove files associated to 6981 simplify format of files for 2033 and 5108
simplify code of tasks 2033, 5108, 6956, 7225 add task 4972 about implementing own interfaces
rework source code of task 5108 to clarify error if program failed on writing file