Special character like ampersand not accepted on email subject

Describe the bug

When using special character (ampersand, quote, double quote etc...) the email subject is displaying them as escaped. The email subject is not HTML IMHO, therefore HTML elements should not be escaped and should be displayed.

To Reproduce

1. Create a particpatory space and use an ampersand in the name (like "Example & co")
2. Create a proposal module and submit a proposal with the following title: "Proposal & else"
3. Check the mail, it should have the following subject: "New proposal "Proposal & else" in Example & co"

Expected behavior

As a user I expect the email subject to be "New proposal "Proposal & else" in Example & co"