Automatically fill the "label" field when it has not been filled by the user

In the new WYSIWYG editor, when creating a link towards an attachment, the user is currently expected to fill the "label" field. Not doing so results in a JS error to be thrown. This behavior will make the user freak out.

In order to improve this situation, the suggested solution is the following:

• On the "Edit link parameters", automatically input the filename as a label (the user can edit it)
• If the user chooses to edit a link pointing towards an attachment, implement the following check:
  • If the label is the same as the finename -> update the label with the name of the new file
  • If the label differs from the filename -> keep the label