improve the whatsnew section

the link to JBT versions should open a new page, not just expand the menu. They could link to the first component in the list of N&N.
The N&N for a given version (.Alphax, .BetaX, .CRx) could be a single page using Bootstrap scrollspy to track scrolling a provide anchors (ie, URLs) that the users could share.

For the .Final version, a merge of all N&N per component could be interesting.