Improve multivalued and adapt to sunburst


* We can set as false a parameter on widget: actb_multivalued_adding_is_required,
  so that if user hasn't clicked 'add' button on a multivalued field,
  current input is considered as a new value.
  Improves user experience when vocabulary is not enforced.

* Added a property in site_properties to define custom separators.
  "," is set as a custom separator by default. ";" is always a separator.

* Fixed: was unusable out of the box with default sunburst theme.

* Consider, by default, lines fields as multiValued fields.