Invoice addresses: Ask for a state in some countries (#1362)

* Invoice addresses: Ask for a state in some countries

* API, tests, noscript

* Fix shredder tests

* Add test for addresses with long state names

src/pretix/base/views/js_helpers.py

@@ -0,0 +1,16 @@
+import pycountry
+from django.http import JsonResponse
+
+from pretix.base.settings import COUNTRIES_WITH_STATE_IN_ADDRESS
+
+
+def states(request):
+    cc = request.GET.get("country", "DE")
+    if cc not in COUNTRIES_WITH_STATE_IN_ADDRESS:
+        return JsonResponse({'data': []})
+    types, form = COUNTRIES_WITH_STATE_IN_ADDRESS[cc]
+    statelist = [s for s in pycountry.subdivisions.get(country_code=cc) if s.type in types]
+    return JsonResponse({'data': [
+        {'name': s.name, 'code': s.code[3:]}
+        for s in sorted(statelist, key=lambda s: s.name)
+    ]})