Correctly call backend with continuation for treenode link
Correctly call backend with continuation for treenode link

The function is corrected for a missing continuation and
now correctly updates the treenode display after joining
(it does a complete refresh, refetching all nodes)

fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID