Provide Performance Platform report as Excel file

This is the format we need to upload it in, so this means not having to
manually re-save it as Excel.

app/utils.py

@@ -4,7 +4,7 @@ import re
 import unicodedata
 from datetime import datetime, time, timedelta, timezone
 from functools import wraps
-from io import StringIO
+from io import BytesIO, StringIO
 from itertools import chain
 from os import path
 from urllib.parse import urlparse
@@ -12,6 +12,7 @@ from urllib.parse import urlparse
 import ago
 import dateutil
 import pyexcel
+import pyexcel_xlsx
 import yaml
 from flask import abort, current_app, redirect, request, session, url_for
 from flask_login import current_user
@@ -278,6 +279,20 @@ class Spreadsheet():
         pyexcel.free_resources()
         return instance
 
+    @property
+    def as_rows(self):
+        return list(csv.reader(
+            self.as_csv_data.strip().splitlines(),
+            quoting=csv.QUOTE_MINIMAL,
+            skipinitialspace=True,
+        ))
+
+    @property
+    def as_excel_file(self):
+        io = BytesIO()
+        pyexcel_xlsx.save_data(io, {'Sheet 1': self.as_rows})
+        return io.getvalue()
+
 
 def get_help_argument():
     return request.args.get('help') if request.args.get('help') in ('1', '2', '3') else None