Merge new Select2 widget into old suggestion widgets

The idea is to replace in existing widget templates the templates of select2 mainly in edit mode. This is true for:

• User Suggestion (Single / Multiple)
  We delete the widget type and we do what's necessary to make existing single_user_suggestion and multiple_user_suggestion fallback on select2 in edit mode
• Document Suggestion (Single / Multiple)
  idem

Plus, rename Select2Directory and Select2MultipleDirectory to suggestOneDirectory and suggestManyDirectory. These two new widget types will come in addition of the existing selectOneDirectory and selectManyDirectory