do not store GroupOrderArticles with zero quantity and tolerance

Conflicts:
	app/models/group_order_article.rb
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remove outdated group_order left-overs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
group_order fixes
no popover (revert part of 602a03c9e10d153d57d6307b85c8d52acddc264e)