New files :
* classic_poll.js -> loaded on page choix_autre.php
* date_poll.js -> loaded on page choix_date.ph
* framadatepicker.js -> loaded on pages that need the date picker

* Utils::issetAndNoEmpty is now removed
* Use Form object to store value from page to page

bug correction on email notification (using '$dsondage->titre' in adminstuds.php)

handle date format for windows platform

new variable $user_can_add_link_or_url to choose if the http link can be displayed during poll creation

dynamic usage of the $default_poll_duration variable to display coherent information to user.

Accessibilité et ergonomie sur choix_date, adminstuds - remplacement bouton de langue par un select - Fix export CSV - découpage chaines de langue pour enlever le code html - Fix // et port dans get_server_name