position_controller task added and small changes in describtion of the other tasks

...scripts/controller/controller_task/position_controller.py

...ipts/controller/controller_task/position_controller.ipynb

...ion_scripts/move_it/move_it_basics/move_it_basics_3.ipynb

...ion_scripts/move_it/move_it_basics/move_it_basics_4.ipynb

...n_scripts/move_it/move_it_objects/move_it_objects_1.ipynb

...n_scripts/move_it/move_it_objects/move_it_objects_2.ipynb

...n_scripts/move_it/move_it_objects/move_it_objects_3.ipynb

..._ws/src/learn_environment/task_pool/task_definitions.json