option to add multiple elements in basic view

[pvgenuchten]

Goal of basic view is to have a very simple editor with only required fields, therefore some "add element" buttons are hidden if an instance of an element already exists. For the following elements we would like to see the add button anyway:

• keyword (already existing in the new software),
• date (so you can add creation and publication date for example)
• contact (so we can add multiple contacts).