Improve MENUITEMS in settings

[freezed]

This constant is a bit confusing and might mix some pelican option :

pythonclassmates.org/pelicanconf.py

Line 19 in d8270c8

MENUITEMS = [

See basic-settings

Options :

1. Use USE_FOLDER_AS_CATEGORY, and do not use categories in article metedata
2. Use DISPLAY_PAGES_ON_MENU, and not hardlinking to a category/*.htmllike this : ('Tutoriels', '/category/tutoriels.html'),