Field show_menu generates three menus Introduction, Location and Register on the
page of the event on the website.
Generating new menus requires the Technical Features groups so checking this box
would produce and error on non-technical users.
Moreover these menus are hardcoded, making it less useful and may produce
unexpected behaviour (replaces previous menus).
Hide the menus to non-technical users and add help message explaining the
effect of the field.
Fixes#7099
Martin Trigaux
ad00496a41