Provide a "footnotes" block collecting all definitions present on a page

Current stage:

• JS code to transform the links is WIP in class G2Footnotes
• source links are replaced by a.name anchors
• source links have a footnote fragment link in a sup element appended
• block is available, with static content

Next steps

• generate the links in the footnotes block as an unnnumbered list because there can be multiple source backlinks in any given footnote link
• generate the backlinks from the block to the source links
• add CSS styling for the sup elements
• add automatic triggering with Drupal behaviors
• add tests (Nightwatch ?)
• convert to web component. Example in Acquia DAM

Actually, this is vanilla JS, no jQuery. And being worked on at DDD Vienna.

Merged to current dev HEAD.

Some limitations remain:

• DFN links dynamically added after the footnotes block is generated will not be updated and appear on the footnotes block: there are TODO in the code about this
• The Gitlab eslint step fails because it cannot find airbnb-base, but yarn lint passes locally.

So at this point it is better to merge than to keep.

Automatically closed - issue fixed for 2 weeks with no activity.