Make a function for parsing help query param

Our templates are a littered with `request.args.get('help', '0')`.
This commit refactors these into a single helper method, which can be
used by the view functions, then passed to the template.

This makes the templates cleaner, and should make it easier to refactor
`help` out of the query parameters entirely in the future.

app/utils.py

@@ -186,3 +186,7 @@ class Spreadsheet():
             file_type=extension,
             file_content=file_content.getvalue()
         ).to_array(), filename)
+
+
+def get_help_argument():
+    return request.args.get('help') if request.args.get('help') in ('1', '2', '3') else None