Refined UI, added solution execution and reset buttons for robot and notebook

...ironment/include/learn_environment/notebook_converter.hpp

...rn_environment/include/learn_environment/subtask_item.hpp

...n_environment/include/learn_environment/task_executor.hpp

...rn_environment/include/learn_environment/task_manager.hpp

catkin_ws/src/learn_environment/resource/icons/help.png

catkin_ws/src/learn_environment/resource/icons/play.png

catkin_ws/src/learn_environment/resource/icons/robot.png

catkin_ws/src/learn_environment/resource/icons/stop.png

...in_ws/src/learn_environment/resource/learn_environment.ui

catkin_ws/src/learn_environment/resources.qrc

catkin_ws/src/learn_environment/src/custom_list_widget.cpp

catkin_ws/src/learn_environment/src/learn_environment.cpp

catkin_ws/src/learn_environment/src/notebook_converter.cpp

catkin_ws/src/learn_environment/src/process_runner.cpp

catkin_ws/src/learn_environment/src/subtask_item.cpp

catkin_ws/src/learn_environment/src/task_executor.cpp

catkin_ws/src/learn_environment/src/task_manager.cpp