In the form to become a new cooperator, the field info_session_confirmed
was required but not in the form validation. This commit fixes that
incoherence but changing the form to let field info_session_confirmed
not required.
This adds, in the new cooperator form in the website, a checkbox that
the user can check if he already has taken part to an information
session.
This information will be saved in the partner object and will be used to
automatically check the info_session field of the cooperator_status when
it will be created by the wizard.