Consistent use of plt in ex2

exercises/02450Toolbox_Python/Scripts/ex2_1_1.py

exercises/02450Toolbox_Python/Scripts/ex2_2_1.py

exercises/02450Toolbox_Python/Scripts/ex2_2_2.py

exercises/02450Toolbox_Python/Scripts/ex2_3_1.py

exercises/02450Toolbox_Python/Scripts/ex2_3_2.py

exercises/02450Toolbox_Python/Scripts/ex2_3_3.py

exercises/02450Toolbox_Python/Scripts/ex2_3_4.py

exercises/02450Toolbox_Python/Scripts/ex2_3_5.py

exercises/02450Toolbox_Python/Scripts/ex2_3_6.py

exercises/02450Toolbox_Python/Scripts/ex2_3_7.py

exercises/02450Toolbox_Python/Scripts/ex2_4_1.py

exercises/02450Toolbox_Python/Scripts/ex2_4_2.py