Refs #99 -- Improve support for currencies with less than 2 decimal places (#783)

* Refs #99 -- Fix stripe support for zero-decimal currencies

* Add new money formatting method

* Force decimal places in many places

* Locale-aware currency rendering

* Fix currencies in more places

* More currency fixes

src/pretix/control/forms/item.py

@@ -17,6 +17,7 @@ from pretix.base.models import (
 from pretix.base.models.items import ItemAddOn
 from pretix.control.forms import SplitDateTimePickerWidget
 from pretix.control.forms.widgets import Select2
+from pretix.helpers.money import change_decimal_field
 
 
 class CategoryForm(I18nModelForm):
@@ -159,6 +160,7 @@ class ItemCreateForm(I18nModelForm):
 
         self.fields['category'].queryset = self.instance.event.categories.all()
         self.fields['tax_rule'].queryset = self.instance.event.tax_rules.all()
+        change_decimal_field(self.fields['default_price'], self.instance.event.currency)
         self.fields['tax_rule'].empty_label = _('No taxation')
         self.fields['copy_from'] = forms.ModelChoiceField(
             label=_("Copy product information"),
@@ -292,6 +294,7 @@ class ItemUpdateForm(I18nModelForm):
             'over 65. This ticket includes access to all parts of the event, except the VIP '
             'area.'
         )
+        change_decimal_field(self.fields['default_price'], self.event.currency)
 
     class Meta:
         model = Item
@@ -345,8 +348,29 @@ class ItemVariationsFormSet(I18nFormSet):
             return False
         return form.cleaned_data.get(DELETION_FIELD_NAME, False)
 
+    def _construct_form(self, i, **kwargs):
+        kwargs['event'] = self.event
+        return super()._construct_form(i, **kwargs)
+
+    @property
+    def empty_form(self):
+        self.is_valid()
+        form = self.form(
+            auto_id=self.auto_id,
+            prefix=self.add_prefix('__prefix__'),
+            empty_permitted=True,
+            locales=self.locales,
+            event=self.event
+        )
+        self.add_fields(form, None)
+        return form
+
 
 class ItemVariationForm(I18nModelForm):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        change_decimal_field(self.fields['default_price'], self.event.currency)
+
     class Meta:
         model = ItemVariation
         localized_fields = '__all__'
@@ -399,7 +423,6 @@ class ItemAddOnsFormSet(I18nFormSet):
 
 class ItemAddOnForm(I18nModelForm):
     def __init__(self, *args, **kwargs):
-        self.event = kwargs.pop('event')
         super().__init__(*args, **kwargs)
         self.fields['addon_category'].queryset = self.event.categories.all()