Add documentation property to details view

[AxelRICHARD]

Add a textarea widget in Details view for all SysMLv2 elements (except for Documentation itself), allowing to add/edit a documentation for the selected element.
This widget will only handle the first documentation associated to the selected element.
If no documentation is associated to the selected element, then a new value in this widget will also create a Documentation element and will associate it to the selected element.