support editing of nested categories

Conflicts:
	Gemfile
	Gemfile.lock
	app/assets/stylesheets/application.css
	app/views/article_categories/_form.html.haml
	app/views/article_categories/index.html.haml
	db/schema.rb
use nested categories in ordering screen
also show categories with only children
use categories in select boxes

Conflicts:
	app/views/articles/sync.html.haml
fix edit nested category also for rails 3
enter in pc or units in current_orders articles
vokomokum: use user.id for uploading, only upload for user ids < 20000
vokomokum: settle order without charging accounts; closes foodcoop-adam#114
vokomokum: use ID_OFFSET
add default user settings to configuration
use group display method more
vokomokum: use ordergroup ID when calling upload_amounts
vokomokum: add CSV export button
fix Vokomokum CSV export with multiple orders
vokomokum: batch upload amounts when finishing order
vokomokum: batch upload amounts when finishing order (2)
handle vokomokum exceptions
fix vokomokum order close error
fix vokomokum order closing typos
show deleted groups differently