Easier PCI DSS compliance for payment pages (#4273)

* Assign names to compressed scripts

* Make PCI-relevant pages detectable

* Make payment summary markup more consistant to easy work in tracking plugin

* Add docs note

src/tests/testdummy/signals.py

@@ -26,6 +26,7 @@ from pretix.base.signals import (
     register_payment_providers, register_sales_channel_types,
     register_ticket_outputs,
 )
+from pretix.presale.signals import html_head
 
 
 @receiver(register_ticket_outputs, dispatch_uid="output_dummy")
@@ -61,3 +62,11 @@ class FoobarSalesChannel(SalesChannelType):
 @receiver(register_sales_channel_types, dispatch_uid="sc_dummy")
 def register_sc(sender, **kwargs):
     return [FoobarSalesChannel, FoobazSalesChannel]
+
+
+@receiver(html_head, dispatch_uid="dummy_html_head")
+def html_head_presale(sender, request=None, **kwargs):
+    if getattr(request, 'pci_dss_payment_page', False):
+        # No tracking scripts on PCI DSS relevant payment pages
+        return ""
+    return "<script>alert('BAD TRACKING SCRIPT')</script>"