make orders helpers clearer

Conflicts:
	app/helpers/orders_helper.rb
	app/views/orders/_articles.html.haml
give partially unused order articles a distinct colour

Conflicts:
	app/assets/stylesheets/bootstrap_and_overrides.css.less
use new Mollie API
add payment details to financial transactions
show payment details in finance + ordergroup home
allow to skip notification after transaction
use financial transaction payment details with Mollie API
Support more complex Mollie transaction fees.
fix signup plugin after transaction change
fix Mollie buglets
show proper error when all articles are deselected in order edit
add pickup day to orders
first iteration
use affix for article info box
use proper form field names + show goa values
ui improvements
add shopping cart
move ordering to group_order; redesign archive

decided that the faceted browser view belongs to the group_order
view/controller; also bring the group-order in line
separate group_orders show and edit
fix query performance