New plugin statiegeld_tokens

Activating statiegeld_tokens will limit the use of the statiegeld plugin
for container deposit refunds to what was bought at this venue.

Still needs documentation.

Changes to 'statiegeld' and 'undo' were made to support the new
plugin, specifically:

- metadata (attributes) added in $cart->add, for the statiegeld_tokens
  plugin to use.
- statiegeld plugin now shares a global variable (configuration).
- undo can now be rolled back during hook_checkout.

plugins/statiegeld

@@ -18,7 +18,7 @@ use List::Util;
 # (Note that the Dutch term "statiegeld" should only be displayed if you
 # choose to use it in the product descriptions.)
 
-my @addon_accounts = ("+statiegeld");
+our @addon_accounts = ("+statiegeld");
 my $nope = "Sorry, no deposit on that product.\n";
 
 my $S = ($ENV{REVBANK_STATIEGELD} // 0) == 1;
@@ -28,7 +28,7 @@ sub command ($self, $cart, $command, @) {
 
 	defined &RevBank::Plugin::products::_read_products
 		or die "statiegeld plugin requires products plugin";
-	
+
 	my $products = RevBank::Plugin::products::_read_products();
 	my $product = $products->{$command} or return NEXT;
 
@@ -55,7 +55,7 @@ sub command ($self, $cart, $command, @) {
 		my $d = "$addon->{description} ($product->{description})";
 
 		$cart
-		->add(+$addon->{price}, $d)
+		->add(+$addon->{price}, $d, { plugin => $self->id, addon_id => $addon->{id} })
 		->add_contra($addon->{contra}, -$addon->{price}, "$d for \$you");
 	}