At the moment the file contents are not persisted by checked in
memory.
The first and last three records are show if all are valid.
If there are invalid rows, they are reported and the user is
prompted to go back and sort out upload file.
The storing of upload result (i.e. validation of file) in session
will be removed in next story which is about persisting of file
for later processing.
This commit:
- replaces links that look like buttons with forms and submit buttons
- splits the view code for SMS into its own file
- moves the routing into the Python by adding handling for `post` requests
- uses Flask’s `url_for` to generate URLs, rather than hard coding them (so that
it’s easier to change the URLs)
- chages the URLs for sending text messages
