Refactor payment QR code generation code and add SPAYD format (#5680)

Move generation of QR code contents out of the HTML template and into Python code, so it can
be reused in plugins and tested with unit tests. Add the SPAYD QR code format which is used in
Czech Republic and Slovakia [1]. Display BezahlCode QR codes only for German IBANs.

[1] https://en.wikipedia.org/wiki/Short_Payment_Descriptor

src/pretix/presale/templates/pretixpresale/event/payment_qr_codes.html

@@ -0,0 +1,44 @@
+{% load i18n %}
+{% load static %}
+
+{% if payment_qr_codes %}
+    <div class="tabcontainer col-md-6 col-sm-6 hidden-xs text-center js-only blank-after">
+        <div id="banktransfer_qrcodes_tabs_content" class="tabpanels blank-after">
+            {% for code_info in payment_qr_codes %}
+                <div id="banktransfer_qrcodes_{{ code_info.id }}"
+                    role="tabpanel"
+                    tabindex="0"
+                    {% if not forloop.first %}hidden{% endif %}
+                    aria-labelledby="banktransfer_qrcodes_{{ code_info.id }}_tab"
+                >
+                    {% if code_info.link %}<a aria-label="{{ code_info.link_aria_label }}" href="{{ code_info.link }}">{% endif %}
+                    <div class="{{ code_info.css_class }}" role="figure" aria-labelledby="banktransfer_qrcodes_{{ code_info.id }}_tab banktransfer_qrcodes_label">
+                        {{ code_info.html_prefix }}
+                        <script type="text/plain" data-size="150" data-replace-with-qr data-desc="{% trans 'Scan this image with your banking app’s QR-Reader to start the payment process.' %}">{{ code_info.qr_data }}</script>
+                    </div>
+                    {% if code_info.link %}</a>{% endif %}
+                </div>
+            {% endfor %}
+        </div>
+        <div id="banktransfer_qrcodes_tabs" role="tablist" aria-labelledby="banktransfer_qrcodes_label" class="blank-after btn-group">
+            {% for code_info in payment_qr_codes %}
+                <button
+                    class="btn btn-default"
+                    id="banktransfer_qrcodes_{{ code_info.id }}_tab"
+                    type="button"
+                    role="tab"
+                    aria-controls="banktransfer_qrcodes_{{ code_info.id }}"
+                    aria-selected="{{ forloop.first|yesno:"true,false" }}"
+                    tabindex="-1">{{ code_info.label }}</button>
+            {% endfor %}
+        </div>
+        <p class="text-muted" id="banktransfer_qrcodes_label">
+            {% trans "Scan the QR code with your banking app" %}
+        </p>
+    </div>
+    {% for code_info in payment_qr_codes %}
+        {% if code_info.id == "qrbill" %}
+            <link rel="stylesheet" href="{% static "pretixplugins/banktransfer/swisscross.css" %}">
+        {% endif %}
+    {% endfor %}
+{% endif %}