can now create upstream to downstream direct connections
unrelevant list elements are grayed-out

grey out Calculate button if basins structure is invalid
use Mermaid Nodes for walls
suffix multiple walls on same basins pair
base Mermaid Nodes on children UIDs
display Mermaid code (debug)
unselect element after deletion
highlight selected element

add basin
remove basin (buggy)
remove wall

Refs #338

strip browser language to 2 letter lowercase code

update Espece translations for PAR
update doc for PAR verification