Fix memory usage in exporters by using chunked iterators

src/pretix/helpers/iter.py

@@ -0,0 +1,10 @@
+import itertools
+
+
+def chunked_iterable(iterable, size):
+    it = iter(iterable)
+    while True:
+        chunk = tuple(itertools.islice(it, size))
+        if not chunk:
+            break
+        yield chunk