Email template fixes

[ihsaan-ullah]

@ mention of reviewers

@Didayolo

A brief description of the purpose of the changes contained in this PR.

• Codabench logo was not working in the emails, now fixed
• Slight changes to the email text
• Unsubscribe link removed because we don't have unsubscribe functionality

Issues this PR resolves

• 1460

A checklist for hand testing

We need to deploy this change on codabench test for testing

Checklist

• [x] Code review by me
• [ ] Hand tested by me
• [x] I'm proud of my work
• [x] Code review by reviewer
• [ ] Hand tested by reviewer
• [x] CircleCi tests are passing
• [ ] Ready to merge

[Didayolo]

@ihsaan-ullah Thanks for the PR. Why do we have for each email template a .html file and a .txt file with the same content?

[ihsaan-ullah]

I missed some email templates. Now all ara changed

[ihsaan-ullah]

@ihsaan-ullah Thanks for the PR. Why do we have for each email template a .html file and a .txt file with the same content?

For some reason, both txt and html files are used to send the emails https://github.com/codalab/codabench/blob/a37139a96d7f2beb169b40e9e322453545be5673/src/utils/email.py#L9

[Didayolo]

@ihsaan-ullah Deployed on codabench-test.lri.fr

[ihsaan-ullah]

Emails sent to participants are working. For some reason I am not receiving admin emails (sent to organizers)

[ihsaan-ullah]

We can improve the email design in the future