better re-use of accept_invitation form

(complements 083d1dcb6d7ab9c03f11c74ea30a60f294db7f43)
improve signup
Bumped new version: 3.3.2-adam
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
small group_order ui update
fix group_orders archive
start to make ordering work :)
only show articles I ordered in shopping cart
make ajax ordering work
remove outdated group_order left-overs
make tests work again
introduce units filled progress bar