If number of guests is 255 (which is the default value), no email will be sent
to the recepient. Most normal users have Javascript enabled, so their browser
should throw an error if the number of guests isn't filled out.
This commit contains the following changes:
* Better error handling: Previously, there was no proper handling in
of email-related errors. Now, all error messages are caught and the
user gets a nice landing page. The script will always try to contact
the organizers of the wedding with information on the error.
* Emails for not-attending: This commit adds the possibility to send
seperate emails to guests that attend and guests that cannot attend.
* Language strings for JavaScript errors: Previously, all JS errors were
in Dutch. Now, they are configurable.
This commit includes a fully functional template and Rust backend. The
website is able to send e-mails, displays strings in multiple languages,
include attachments, and has basic protection again spam (IP based).
