Linkeditor layout

[brichet]

This PR is a first iteration on the LinkEditor layout and features.

It includes the 3 panels of the editor (Linked Dataset, Linking and Summary). In this PR, the Linked Dataset widget only allows to select dataset, which displays the list of attributes in the Linking widget. The Linking widget allows to select attributes, but does not glue these attributes yet.

The next steps should probably be done in follow up PRs:

• gluing attributes using kernel
• displaying glued dataset in Linked Dataset widget
• displaying glued attributes in Summary widget
• including advanced link

[github-actions[bot]]

:point_left: Launch a Binder on branch _brichet/glue-lab/linkeditorlayout

[GabrielaVives]

It's looking good ! I don't have particular comments for the moment. I will spend time on the UI design (at the time I had only considered the UX of this, I didn't go deep into UI considerations) of the link editor for the next PR. For example the colours, the tabs design, and the titles of each section.

[brichet]

Thanks @trungleduc, I integrated your suggestions.

[trungleduc]

Thanks @brichet