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/pretix/plugins/stripe/templates/pretixplugins/stripe/presale_head.html

@@ -2,10 +2,10 @@
 {% load compress %}
 {% load i18n %}
 
-{% compress js %}
+{% compress js file stripe %}
     <script type="text/javascript" src="{% static "pretixplugins/stripe/pretix-stripe.js" %}"></script>
 {% endcompress %}
-{% compress css %}
+{% compress css file stripe %}
     <link type="text/css" rel="stylesheet" href="{% static "pretixplugins/stripe/pretix-stripe.css" %}">
 {% endcompress %}
 {% if testmode %}