Use the correct bucket for storing contact lists

We don’t want to muddy them up with the normal CSV uploads.

I’ve tried to reuse the existing S3 code where possible because it’s
well tested.

Buckets have already been created.

app/utils.py

@@ -323,6 +323,13 @@ class Spreadsheet():
         pyexcel.free_resources()
         return instance
 
+    @classmethod
+    def from_file_form(cls, form):
+        return cls.from_file(
+            form.file.data,
+            filename=form.file.data.filename,
+        )
+
     @property
     def as_rows(self):
         if not self._rows: