We were previously persisting the logo for the email branding and
deleting the temp files that get created before trying to update the
database with the new email branding. This meant that if there was an
error when saving (e.g. the domain used was a duplicate) the final logo
was already in S3 and trying to go 'back' in the browser would give an
error since the temp files needed to display the create branding page
had already been deleted.
This changes the order we do things in, so that we try persisting the
email branding to the database first.
Storing things in the session is proving buggy – we still have one user
(that we know about) where the session data isn’t getting written, so
they’re blocked from uploading a file.
Since all the info we’re storing in the session is about the file, it
makes sense to store it with the file.
This commit only does the writing of the metadata, once we’re sure this
is working we can do subsequent work to read it back, and remove
reliance on the session.
Done using isort[1], with the following command:
```
isort -rc ./app ./tests
```
Adds linting to the `run_tests.sh` script to stop badly-sorted imports
getting re-introduced.
Chosen style is ‘Vertical Hanging Indent’ with trailing commas, because
I think it gives the cleanest diffs, eg:
```
from third_party import (
lib1,
lib2,
lib3,
lib4,
)
```
1. https://pypi.python.org/pypi/isort
