This is for consistency with how we do it for filenames in the previous
commit and moves the decoding into the `LetterMetadata` class for
abstracting this behaviour.
Small refactor of the LetterMetadata class needed to handle None case as
recipient can be None.
S3 can only handle ascii characters, therefore for filename which could
include non ascii characters, for example a filename with the character
'£' in it, we must encode these using urllib before saving it as s3
metadata. We then also make sure that it comes back decoded when
presenting it to the user.
S3 metadata only supports ascii characters. Whenever we save data to it
we need to make sure we encode it to save it and then decode it to
display it again to users. This abstraction will act as the place for
that decoding to happen so the rest of the code in our views doesn't
need to care about the encoding abstraction.
Now persisting the address to the "to" field of the Notification, after the notification has been validated.
If the letter is pending validation, then "Checking..." will appear as the identifier for the letter.
If the letter has passed validation, then the first line of the address (now persisted in the "to" field) will be displayed, with the client reference underneath.
If the letter has failed validation the "Provided as PDF" will show be displayed, which is now the initial value of the "to" field.
The recipient of the letter now displays at the bottom of the page when
previewing a valid letter. The template preview `/precompiled/sanitise`
endpoint returns the address, but we format it to display on a single
line with commas between each line. We also need to convert the
recipient address to ASCII so that it can be stored as S3 metadata.
We had been storing whether or not a file was valid in the S3 metadata,
but using the query string of the URL to store the original filename
and the page count. This meant that if you tried to view the preview
letter page without the query string you would see a `500`. It was
possible for this to happen if you were signed out of Notify while on
the preview page - you would be redirected back to the preview page but
without the query string, causing an error.
This sanitises uploaded letters and stores the sanitised result in S3
with if it passes validation or the original PDF in S3 if validation
fails. A metadata value of 'status' is set to either 'valid' or
'invalid'.
