Project to automatically send marks to students from a summary in a .csv file.
(And trying to learn about Git in the same time.)

The data should be stored in a CSV file which 3 first columns and 4 first lines
are reserved space (template given). All other columns are taken to be topics,
all other lines are taken to be students. The program can manage empty cells.
(Don't know if empty columns are considered as topic.)

Call the program with
    python main.py path/to/file.csv


TODO: maybe try to transform the gui function into a SelectionInterface class
TODO: the dictionary building part in 'retrieve_marks' could be removed.
    (I prefered to keep it on case, but it could be retrieved from previous
    commits).
TODO: The function actually sending the mail is still to be done.
    But there is a function printing the mail instead of writting them
    (dry-run).
TODO: option for dry-run (parser in main ?)
TODO: behaviour of ABORT button in SelectionInterface (quit all the program) ?
    (care with its docstring then)