Add vendor-event link parameter: cash
Split order info & payment in 2 pages

When the order is opened, a dashboard incl. payment registration is
shown. Order info is also summarised in the dashboard with a [edit]
link next to it. Order info is no longer accessible from the menu.
Update "Organised by" table with payment methods

Solves #239
Cash + card icon are shown if these are filled in the links table:
vendors x events 1 main|cash
vendors y events 1 sales|cash|card