On a contribution preview, add a 'Signal problem' button

[woecifaun]

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On the contribution preview page (http://haphpy-birthday.net/en/contribution/t/Woecifaun), add a simple system to report issue with the contribution.

It could be

• a simple link Report an issue with this contribution
• displaying a simple textarea and a submit button.
• a Captcha preventing spam
• an explanation about moderation and what will (or not) be done

Ideas on the fly:

• No email address required. People wanting to be contacted back can add it in the message.
• Better inform user that the request will be handled but the decision is remains HaPHPy Birthday's team.