Accept common spreadsheet formats, not just CSV

We require users to export their spreadsheets as CSV files before
uploading them. But this seems like the sort of thing a computer should
be able to do.

So this commit adds a wrapper class which:
- takes a the uploaded file
- returns it in a normalised format, or reads it using pyexcel[1]
- gives the data back in CSV format

This allows us to accept `.csv`, `.xlsx`, `.xls` (97 and 95), `.ods`,
`.xlsm` and `.tsv` files. We can upload the resultant CSV just like
normal, and process it for errors as before.

Testing
---

To test this I’ve added a selection of common spreadsheet files as test
data. They all contain the same data, so the tests look to see that the
resultant CSV output is the same for each.

UI changes
---

This commit doesn’t change the UI, apart from to give a different error
message if a user uploads a file type that we still don’t understand.

I intend to do this as a separate pull request, in order to fulfil
https://www.pivotaltracker.com/story/show/119371637

app/main/validators.py

@@ -1,6 +1,7 @@
 import re
 from wtforms import ValidationError
 from notifications_utils.template import Template
+from app.utils import Spreadsheet
 
 
 class Blacklist(object):
@@ -20,8 +21,8 @@ class CsvFileValidator(object):
         self.message = message
 
     def __call__(self, form, field):
-        if not field.data.filename.lower().endswith('.csv'):
-            raise ValidationError("{} is not a CSV file".format(field.data.filename))
+        if not Spreadsheet.can_handle(field.data.filename):
+            raise ValidationError("{} isn’t a spreadsheet that Notify can read".format(field.data.filename))
 
 
 class ValidEmailDomainRegex(object):

app/main/views/send.py

@@ -27,7 +27,7 @@ from app.main.uploader import (
     s3download
 )
 from app import job_api_client, service_api_client, current_service, user_api_client, statistics_api_client
-from app.utils import user_has_permissions, get_errors_for_csv
+from app.utils import user_has_permissions, get_errors_for_csv, Spreadsheet
 
 
 def get_send_button_text(template_type, number_of_messages):
@@ -112,10 +112,7 @@ def send_messages(service_id, template_id):
             s3upload(
                 upload_id,
                 service_id,
-                {
-                    'file_name': form.file.data.filename,
-                    'data': form.file.data.read().decode('utf-8')
-                },
+                Spreadsheet.from_file(form.file.data.filename, form.file.data).as_dict,
                 current_app.config['AWS_REGION']
             )
             session['upload_data'] = {