[example/Waspello] Implement functionality behind "Add card" and "Copy list" List actions

Right now we have three list actions available in the list menu, which pops up when user clicks on three dots in corner of the list:

"Delete this list" works, but the other two ("Add card" and "Copy list") have not been implemented it yet. It should be fairly straightforward to add this functionality. Although maybe it would be nicer to first take care of #334 before going into adding more features, but on the other hand this wouldn't introduce any new conceptual complexity.