Feature/notifications

See merge request zesje/zesje!106

Currently we secure deployments using auth enforced by the
frontend server + .htaccess.

closes #244

properly set mimetype on export

Closes #262

See merge request zesje/zesje!105

explicitly remove hashtag from the student number and not the first character

Closes #261

See merge request zesje/zesje!104

Closes #261

1. use a larger scanning area to ensure that barcode fits also if the exam was
   rescaled.
2. if extracting barcode from a downsampled image fails, try the full one

We are careful to try the downsampled images first, so that good scans aren't
impacted.

Separate out saving the file, updating the database, and identifying the
student number.  The last one is implemented such that it can be called outside
of the scanning process (i.e. it only relies on the information that's in the database).

Ensure rubrics get updated when switching between
students or checking/unchecking feedback options

See merge request zesje/zesje!100

factor out email settings into app config

Closes #225

See merge request zesje/zesje!99

Now email will (correctly) fail if either SMTP_SERVER
or FROM_ADDRESS is not set.

Later we will properly warn the user if email is disabled.

Closes #225

This instance was previously overlooked

This is probably a hangover from a refactor. Now the TemplateEditor
component expects the student as a prop and knows when to re-render
itself.