Write exercises for initial chapters

[reingart]

Initial chapters about numbers, strings, conditions and loops don't have proper exercises with automatic grading (just a placeholder with an "Einstein" picture)

Fixing #245 could allow to write simple exercises to give early feedback to students

• https://pyar.github.io/PyZombis/main/lectures/TWP10/TWP10_7.html
• https://pyar.github.io/PyZombis/main/lectures/TWP15/TWP15_6.html
• https://pyar.github.io/PyZombis/main/lectures/TWP17/TWP17_5.html
• https://pyar.github.io/PyZombis/main/lectures/TWP18/TWP18_7.html

Developed excercises should be basic, ideally the same shown in the lectures. For example:

• hello world
• greet (ask the user name and print )
• ask day of birth and print age
• basic string manipulation
• list manipulation, sort, etc.
• conditions (rock, paper, scissors game)
• loops (counter, accumulator, average)