Password resets

The current website has automated password resets. This is done by creating a token, storing a salted, hashed version of this in the database, and then emailing a link that will check the token to the person. A few things to bear in mind:

- ~Tell people to email the webmaster if they haven't updated an old cam address~ (now done)
- ~We could do [e2e testing of this with Mailhog](https://humble.dev/testing-an-email-workflow-from-end-to-end-with-cypress)~ (now done)
- ~If the above is done, we should also test that booking emails and receipts are sent correctly~ (now done)

TODO: We don't nicely handle cases where a password reset is required yet, see below comment for more info.