Rewriting the confirmation message received by people after redirecting

Modify the confirmation text received by contributors to:
- Make it clear in which situations they should contact the organization they redirected towards directly (e.g.: if they want to withdraw their form)
- Include the website of the organization in the e-mail, where it exists and is public

It should be changed in:
- The confirmation e-mail
- The confirmation text on the website after filling the form