show documentation for algorithm boxes on canvas

Maybe a small (i) icon that shows a popup with documentation.

changed milestone to %BP

added C-webui P-medium T-feature labels

mentioned in issue #65 (closed)

mentioned in issue #56 (closed)

mentioned in commit 3c2a9969

mentioned in commit 16299c2f

mentioned in commit 6a8e9e5b

closed via commit 6a8e9e5b

closed via merge request !39 (merged)