Merge branch 'develop' into 'develop'

Added javascript name checking to avoid losing the choices with a bad name

Added a checking on form submit :
 - It cancel form submission if name is empty or doesn't respect the constant NAME_REGEX
 - If the submission is cancelled, it show the error (as a submit would do)

Also added a "header" smarty block in header.tpl, to allow pages which inherit page.tpl to add specific scripts or css.

See merge request !40