Readme: added the contributing git branch

Added in the `README.md` from which branch the contributing users can work.

See merge request !133

Add editorconfig file



See merge request !123

License "CeCILL-B" is not a valid SPDX license identifier

Bonjour,

CeCILL-B n'est pas un identifiant SPDX valide, l'identifiant correct est CECILL-B.
C'est un détail mais ça provoque un avertissement de `composer validate`.

See merge request !121

Fix typo in locale/en.json

Hi,  
Just a minor typofix.  
Kind regards.

See merge request !122

Demande de confirmation lors de la supression d'une colonne.



See merge request !119

Empêcher l'ajout de colonne vide

Fix #123 

- Empêche l'ajout de colonne vide
- Permet la suppression des colonnes vides existantes
- Si l'on a une erreur lors de l'ajout de la colonne , on reste sur le formulaire d'ajout
- Correction de la date pour prendre le bon format par rapport a la langue

See merge request !118

Fix date picker

Fix #154

And more Smarty on poll creation

See merge request !115

Improvement - install

A check.php page before install
Updating config.tpl
Verification of config.php creation at install

See merge request !116

Feature : improve self editing vote

Adding a possibility to the user to enter his email address and to receive the personalized url by email.

See merge request !110

Config.php has bad encoding on install

Fix #142 

See merge request !114

Improvement of the email template to find polls

Fix #78 

See merge request !111